It's true that a great proportion of iPhone games seem to be along the lines of guiding something along using the iPhone's tilt sensors. The rest are games that could have been played on the N64, or even the C64. The iPhone is just too limited a device to allow real innovation. The screen's too small and the interface is too limiting because it' requires you to touch the screen and so obscure the gameplay.
These basic iPhones games will remain popular, but only as gimmicky time killers. If you want real games, you have to go down the DS route and get the iPhone some proper titles that cost proper money. But then you'll want a better interface, and you'll not want calls interrupting you when you're in the middle of battling the end of level boss. In other words, if you can afford an iPhone and want to play great portable games you might as well just buy a DS or PSP.