iPhone uses an elegant development infrastructure. I have seen many architectures in my time, but by making use of the tools and architecture used in the development of Mac OS X, Apple have incrementally cashed in on work they have done before.
This also applies to the AppStore which is an evolution of iTunes into iPhone applications. Using the AppStore as a means of distribution is a very efficient way to get applications to users. In addition Apple have exploited the payment systems developed for iTunes. The really sharp trick however, was to make the licensing of tools inexpensive and so open up access to small studios and independent developers. This has meant the iPhone cashes in on the wealth of creativity in individual developers across the world
Add all that independent creative inspiration and talent to a well designed iPhone platform from a respected manufacturer known for cool design and you can see that it is a potent success recipe.
But like many platforms before, it’s the software developers, not the hardware that really drive the success.