A common fallacy is assuming that any new platform in an exciting market — recently, smartphones and tablet computers — will be flooded with developers as soon as it’s released, as if developers are just waiting outside the gates, hungrily waiting to storm in.

In two recent cases, that’s exactly what happened: the iPhone and the iPad. (And probably the Mac App Store next.) So important people, including the tech press, consumers, and many hardware manufacturers themselves, assume that every new hardware platform will be greeted with the same rush of high-quality software.

Steve Jobs knows this is wrong, even though his company is the beneficiary of the best cases of the supposed effect. As he said, in the recent earnings call:

You’re looking at it wrong. You’re looking at it as a hardware person in a fragmented world. You’re looking at it as a hardware manufacturer that doesn’t really know much about software, who doesn’t think about an integrated product but assumes the software will somehow take care of itself. And you’re sitting around saying, well, how can we make this cheaper? Well, we can put a smaller screen on it, and a slower processor, and less memory, and you assume that the software will somehow just come alive on this product that you’re dreaming up, but it won’t. … Most [developers] will not follow you.

The problem is that hardware manufacturers and tech journalists assume that the hardware just needs to exist, and developers will flock to it because it’s possible to write software for it. But that’s not why we’re making iPhone and iPad software, yet those are the basis for the theory.

We’re making iPhone software primarily for three reasons:

Dogfooding: We use iPhones ourselves. Installed base: A ton of other people already have iPhones. Profitability: There’s potentially a lot of money in iPhone apps.

Of course, the last two are related: it’s hard to have one without the other, but subtle implementation or demographic differences can make a huge installed base yield relatively low profitability.1

Without dogfooding, we aren’t motivated to make our software with craftsmanship and pride.

Without an installed base, too few people will be able to buy our software for it to be worth generalizing and releasing.

Without profitability, we can’t afford to make and support it.

For most platforms, all three conditions need to be met for a significant number of developers to justify writing software for them.2

This worked so well for the iPhone because we already had iPhones for a year before we could make apps for them. Thousands of developers already owned and loved their iPhones: they were so good that we all bought them without having any apps at all. And on day one of the App Store, there were already 6 million iPhones in the world. (Three days later, there were 7 million.) And the app-buying process couldn’t be easier: it was, and remains, the easiest purchasing process in the entire software industry. Dogfooding, installed base, and profitability were all very strong.

The iPad was trickier: it started with an installed base of zero. But the product was so good and so compelling that we all knew that it would sell like crazy from day one. And it was so good that we all got iPads, too, solving the dogfooding issue. And since it retained the same easy purchasing process as the iPhone App Store, and we knew it would have a big installed base shortly, the profitability was promising as well. So a bunch of us made great iPad apps.

Now, consider this fall’s tablet computers. Can you say with confidence that any of them will address these three needs well enough, and for enough developers, to ensure a steady supply of quality software?

I can’t.