A big ebook shoe dropped on Sunday. It dropped on Kobo first. And it has nothing to do with Borders.

Kobo just delivered a new iOS (that’s Apple’s operating system for iPad and iPhone) app that no longer contains the direct link to the Kobo bookstore within it. That means that buying new Kobo books requires going to Kobo.com through the browser (not hard, but additional steps) rather than from a single click from within the app.

Later news on this developing story is that the Google app has been “pulled” and that the Nook Children’s app no longer has a link to the store. We have to expect that the Kindle and main Nook apps will undergo the same change very shortly. That will mean that the simplest and most seamless way to buy and read ebooks on the iPad or iPhone will be through Apple’s iBookstore. It will almost certainly mean a growth in iBookstore market share at the expense of all the other ebook retailers. It will also almost certainly mean that a lot of people who read their ebooks on an iOS device (I’m one of them) and prefer to use any of the other ebook retailers (and I’m one of those too) will be inconvenienced and annoyed.

However, it is also true that Apple will benefit from this move that many of their customers will resent.

The point most emphatically made by all of this is that the book business is a cork floating on a digital device stream. We don’t control our environment. We must keep adapting to what bigger players, some of which have pretty minimal bandwidth to engage us in a dialogue and pretty minimal interest in what’s best from our point of view, see as the best strategy for them.

I have been guilty of a publishing-centric view of the possibility that Apple would enforce the rule that leads to this change since it was first prominently rumored last February. That is: with wishful thinking, when I first heard about this possibility six months ago I thought they wouldn’t do it. I talked myself into believing that because Apple had benefited substantially from the presence of the book apps on their platform, and because there are millions of us who read ebooks on our Apple devices with a distinct preference for using other readers and other ebook stores, that Apple would not enforce the rules which, through a couple of iterations of clarification, say that the way these apps and stores operated was outside their rules.

I will try to remind myself not to be making that mistake again. One of the other big companies recently congratulated me on the ease with which I accept the idea that companies (and people) act in their own self-interest. That’s what Apple has done here.

What this means depends very much on where you sit.

Barnes & Noble (Nook), Google, and Kobo all benefited enormously from Apple’s arrival on the scene in April 2010 because they brought with them the “agency” sales model that leveled pricing across all outlets for the ebooks that come from the biggest publishers. Without agency, many believe (and I’m one of them) that Amazon Kindle’s aggressive loss-leader pricing policies on the biggest books would seriously have diminished the competition.

B&N needs every penny it can spare to invest in device development and marketing; they’d be seriously handicapped if they had to give away margin to compete for consumers.

Google has signed up about 300 independent stores in the US to be partners in its ebook program. They might not have 10% that many if the indies thought they had to compete with loss-leader pricing on the biggest books even to play. When Random House switched over to agency at the beginning of March this past year — 11 months after it began — one of the motivations they cited was to respond to the desire of independent stores to sell ebooks which they heard over and over again depended on agency pricing.

Kobo has always had a global strategy that could enable them to thrive even if they had also-ran status in the US market. But they were trying hard to compete with Amazon pricing in the pre-agency days and as the smallest of the big global ebook players, they would have to be considered the most vulnerable in an environment characterized by loss-leader price warfare.

This change must mean they’ll all lose sales. It is hard to see that it could mean anything else.

Amazon will lose sales too, but they may win overall just because life gets a bit harder for B&N, Kobo, and Google.

All of these retailers have gotten an enormous (but unquantified in data revealed to them) lift from the massive success of iPads and iPhones and the retailers’ ability to access all those devices pretty seamlessly and at no cost. Amazon and Barnes & Noble sold many Kindles and Nooks, of course (Kobo’s device has been a competitor and Google is about to have one), and they’d be selling lots of ebooks if there were no iOS devices. Publishers know that, of the 55-65 percent of their ebooks sales that go to Amazon and 20-30 percent of their ebooks to Barnes & Noble, some of those sales go to the dedicated devices and most of the rest to the iOS devices. But they have no idea what the split is. Now they will start to find out as they see those sales shift from the other retailers to the iBookstore. (Sales to iBookstore, Kobo, Google, and others constitute no more than 15-20 percent of sales and often far less.)

Anyhow, the unambiguous benefit that Apple and the iOS devices used to represent to the retailers is now reduced in value, but agency pricing remains (cheering everybody but Amazon), as does the ability of their customers to use iPads and iPhones to consume their content.

Some publishers will need to reconsider their strategies.

Because Amazon will only allow agency terms to the Big Six publishers (they have ways to offer a competitive 70% share of sales, but they won’t play ball with giving up control of pricing), because some publishers aren’t comfortable with the agency model, and because the iBookstore has not been as aggressive about sourcing content as their competitors (I don’t know this for sure, but it definitely feels like all of the other ebook players have much bigger teams chasing content than iBookstore does), there are publishers selling to the other players and not to Apple. I’d imagine those might be expecting a sudden drop in sales through iOS purchases, although they never actually knew how much of their sales were iOS purchases.

And this points out a big difference between the publishers and the retailers. The retailers know how much of their sales are coming through their app customers. They also know how much of the reading of their ebooks is done on iOS devices. Publishers have no idea. In the longer run, this shows how publishers can benefit if the new players they are creating — Anobii in the UK (who has told us they will share data with publishers) and Bookish in the US (which we have heard less directly will do the same) — get some market share and can provide visibility into consumption that publishers do not have now.

And that takes me back to the book business cork bobbing in the larger digital device stream. There was no ebook business to speak of until Amazon delivered the Kindle device, put massive muscle behind selling it, and used the ability they had then to sacrifice margin to create a powerful commercial proposition that was the catalyst to create the market. There was no serious competition for Amazon until Barnes & Noble’s new management delivered the Nook with an equally powerful commitment to establishing it, using their presence in stores to introduce ebook reading to new audiences and, with further innovation of the devices, contributing to the explosive growth of reading in digital formats.

There was no restraint on Amazon’s ability to use their deep pockets to discount publishers’ content in pursuit of their own market share growth until Apple’s new device, the iPad, created a whole new sales model that forced price stability in the marketplace and, at the same time, handed publishers a new capability to maximize revenue and to use price as a marketing tool.

There was no effective way to introduce book readers to the convenience of digital reading without the investment in a dedicated device until the iPad put the capability into millions of hands that didn’t know they wanted it.

There was no great motivation for ebook retailers to introduce interoperability across devices until many ebook device owners also became iPhone and iPad owners.

We note that all these changes in the marketplace were created by others, not by publishers. That’s not necessarily a bad thing, or even a new thing. Publishers also didn’t spring for the investment that created superstores and then Amazon in the 1990s, all of which increased their sales. A publisher’s role is to use the channels that are available to get books into the hands of readers.

From most publishers’ perspectives, this change might have very little impact. Any iPad or iPhone reader who wants a book can still find and buy one. If the Apple store is strengthened at the expense of Kindle and Nook, that constitutes marketplace diversification that is good for them. (If the impact somehow fell disproportionately on Nook, though, that might not be.)

But the happy symbiosis between the ebook retailers and Apple, by which the retailers got access to customers they would not otherwise have had and Apple was able to readily deliver their customers content they hadn’t otherwise aggregated, appears to have come to an end. And the iBookstore, which had been fighting others for the scraps after Amazon took half or more of the US ebook market and B&N took much more than half the rest, is about to be a much more significant competitor.