Oh, ye of little faith. AP When Apple launched the iPhone 4S instead of the iPhone 5 last week, I initially thought it was a disappointment and a mistake.

If Apple had launched the actual iPhone 5, I thought, they'd have sold more of them.

And that's probably right.

If Apple had launched a radically new iPhone 5, more of the folks who currently own iPhone 4s would have upgraded, so Apple would have sold some more 4S units. As it is, the iPhone 4S is likely to appeal primarily to iPhone 3G and 3GS owners, non-smartphone owners, and non-iPhone owners, most of whom (like me) are presumably stoked to buy the iPhone 4S.

But viewing the 4S as disappointing ignores Apple's likely thinking behind it, which Asymco analyst Horace Dediu explains very clearly here.

The thinking is that most iPhone 4 owners are still bound by the 2-year contracts they had to enter into when they bought the iPhone 4, so they'll be less likely to now upgrade anyway (barring carriers waving those contracts, which they might have if Apple had released the "5").

So the 4S isn't aimed at these folks. It's aimed at the other three categories of iPhone 4S buyers:

Pre-iPhone 4 iPhone users (~70 million of them)

Non-smartphone users (1+ billion, who can now get a 3GS for free, if price is an issue)

Non-iPhone smartphone users (Blackberry, Android, Nokia)

The release of the forthcoming iPhone 5, meanwhile, which presumably will be a more radical upgrade from the iPhone 4, will likely be timed to appeal directly to the ~70 million iPhone 4 owners who will just then be starting to come off their two-year contracts. The iPhone 4 was released in the early summer of 2010. So the two-year window for these contracts will begin to roll off in the summer of 2012 (next June).

As I previously noted, the number of reports about the "iPhone 5" leading up to last week, as well as the specifics about its design (bigger screen, etc.), suggest (to me) that Apple's work on this phone may already be quite advanced.

So it wouldn't be surprising to see Apple launch the phone next June, when the iPhone 4 folks begin to come off their contracts.

In short, Apple's thinking about the iPhone 4S may have been as follows:

It has to be good enough to get iPhone 3G and 3GS users drooling (check)

It has to be good enough to get non-smartphone users to want to upgrade to it or the free 3GS instead of an Android phone (check)

It has to be good enough to get some Android and Blackberry users to switch (check)

And, for good measure, it's possible that Apple even considered fourth and fifth factors about the iPhone 4S:

It has the same form-factor and supply chains as the 4, so it will be easier to ramp production to the desired levels (without having a huge gap in production capacity between the 4 and 4S).

It isn't such-an-amazing-upgrade that the ~70 million iPhone 4 owners stuck with their iPhone 4s for the next year will be pissed that they upgraded a year too soon.

So I shouldn't have considered the iPhone 4S launch disappointing, except for me and other 3GS owners—because we'll get locked into contracts on the 4S and miss the 5. Sure, relative to expectations it was a disappointment, but otherwise it appears to have been typically brilliant.

SEE ALSO: UH OH: Apple Suppliers Say iPhone Orders Weaker Than Expected Because Economy Crappy