1. Make it a rapid-development framework already familiar to some people. These are your first-adopters, and the people that will (in the beginning) get a lot of work with iPhone development, because they have a leg-up on the tools.
2. Make barrier to entry very low to newbies ($100 and an Intel Mac. So from scratch, like $700.)
3. Put $100 Million in front of people looking to develop apps on your platform. Everybody wants a bit of that money, and even a bit of that money is a lot of money.
4. Control distribution and take a percentage off the top. As the thousands of flowers bloom (as a result some of that $100 million, or in pursuit of it), you have a lot of apps you take a chunk out of. I also suspect that the iFund apps will be pretty polished as a result of iFund kind of money. Users get very polished apps at the get go: good first time buying experience leads to repeat sales.
5. Profit

Although the popularity of the iPhone pre SDK certainly doesn't hurt at all.