I thought I had noted this before but don't see it in the archives. The iPhone's popularity is funny because I think people are simply rediscovering the magic of a general purpose computer again. And buying software for those computers. I can't recall the last time I bought software other than Office, TurboTax and maybe Photoshop Elements for my PC or Mac. It's like 1980 again. By describing the iPhone as a phone and not a computer, consumers' expectations were reset and Apple escaped the paradigm of (expensive) boxed software.
With the iTunes system, three important benefits became available: limited piracy, immediacy and low cost (a function of limited piracy, in part).
In brief, the iPhone reintroduced general purpose computers and the world of purchased third-party software to the public after a long absence. Now, the question will be whether the iPhone follows the path of the Apple II or is something new altogether.