The dizzying pace at which US consumers were switching from print to digital couldn’t last forever. Based on the numbers being published by the AAP, with a huge assist in interpretation by Michael Cader at Publishers Lunch, it seems that the slowdown has become very noticeable in the past 12 months.

Between late 2007 when the Kindle came out and late 2011, ebook sales doubled or more every year. Since September 2011, during which Cader reckoned sales were double the year before, the monthly numbers are showing much lower (and declining) year-on-year growth. The April numbers showed only a 37% increase from the year before.

I’ve been pondering this question about when ebooks uptake would slow down for a long time. In March of 2010, 17 months ago, I wrote that my hunch was that the switchover “won’t start slowing down until ebook sales are 20-25% of what a publisher expects on a new title.” And I guessed that would occur before the presidential election of 2012. That feels reasonably consistent with what appears to have happened.

Cader also cites reports from Penguin and Simon & Schuster to document the slowdown. Penguin says ebook sales growth was about 33% in the first half of 2012. And Lunch reports that Carolyn Reidy, CEO of Simon & Schuster, told them she expects about 30% growth in ebook sales during 2012. That would almost certainly constitute their (or anybody else’s) fastest-growing sales channel, but it sure isn’t the annual doubling and tripling (or more) we had seen for several years.

A couple of weeks earlier, Cader dissected the BookStats reporting of publisher sales numbers. As longtime readers of this blog know, what I think is the important metric to watch is “store sales versus online sales”, rather than “print versus electronic”. Store sales are all print, but online sales are not all electronic. The reason I think the channel distinction is more important than the format distinction is because scale is far more useful to deal with retail stores than it is to deal with any online account. The reasons are two: inventory and logistics.

BookStats reports that publisher-direct sales to online retailers — this includes both print and digital, but does not include sales that went through the wholesalers — were about 35% of the total of sales to store and online retailers combined. Online is said to have risen about 35% in the past year and brick stores have declined about 12.6%. My rough math says that the combined total of the two was pretty close to equivalent — down about one percent. Since ebook sales are rising and ebooks are generally cheaper than print books, this passes for “flat”.

The other thing to pay attention to is the difference in ebook sales by type of book. Based on anecdotal evidence, I believe that genre and commercial fiction sales might be approaching half ebook already. (BookStats reports that unit sales of all fiction are currently 64% print and 34% digital.) Narrative non-fiction is about half that. Illustrated books of all kinds are slivers of that.

There are many things we don’t know.

We don’t know how much of the sales growth decline in the past year is due to the publishers’ success at driving up ebook prices. To the extent that’s the cause, we might see the pattern change again when (as I expect) the DoJ settlement is approved and the shackles come off Amazon’s pricing policies.

We don’t know how much of the sales growth decline in the past year might be due to the consumer switchover from dedicated ereaders to multi-function devices that offer them other media and games — and email for that matter — to compete with books. To the extent that’s the cause, the slowdown trend might well be extended because it is likely that a lot of people will switch from eink readers to multi-function devices as those devices continue to get cheaper.

We don’t know to what extent store traffic is affected by the continuing shift of bestsellers, particularly in fiction, to digital consumption. In the short run, there is probably a positive impact on the display space and sales opportunities for illustrated books and children’s books. But, in the longer run, how many stores can survive if the bestseller business continues to move away from them?

We don’t know whether mass merchants will continue to see books as worthy of their shelf space. They sell a lot of genre fiction, which is the most challenged by inexpensive independently-published (and not all of those are self-published) ebooks. And they can switch square footage from one thing to another at great speed and with no sentimentality at all.

But, all in all, the slowdown we’ve seen is good news for the legacy publishing establishment and it will be better news if the trend continues. Anything that slows the decline in brick store market share and the rise in Amazon’s buys time for big publishers and competing retailers to adjust their infrastructures and build new business models that are more effective for the future.

Unfortunately for them, the denouement of this round of DoJ activity is about to give things a sharp shove in the other direction.

If understanding new business models and other new ways for publishers to do their business is important to you, our Publishers Launch Frankfurt event on October 8 should be on your calendar. We are featuring a number of Publishing Innovators from around the world: executives who are inventing those new business models that will enable publishers to thrive in our new digitally-influenced publishing environment.

This conference is worth a post of its own, and it will get it very shortly. But the bottom of this post felt like a good place to point that we are going to feature many outstanding industry- leading publishing executives (and not just from the English-speaking world) who are doing things almost nobody else is. Yet.

And we’ve changed our event time from the normal 9 to 5 to 10:30 to 6:30 to allow people to arrive in Frankfurt on that Monday morning and not miss any of what will be one of the most illuminating events we’ve done.