I think this is an excellent point. Visit the forums on www.toucharcade.com and you'll see legions of kids with iPod Touch devices (no phone contract, the other obstacle to a different widespread mobile platform), but no money to spend on games. There are literally thousands of neat pick-up-and-play games in the App Store for no more than $10, but a large portion of the potential market bitches and whines when anything costs more than 99 cents. I'm no kid and the money is not my primary concern, but the little microtransactions do add up!
Aside from the Sony/Nintendo duopoly, the iPod Touch and iPhone are as close as we get to a mainstream mobile platform. Personally, I'm fine with that, because each device has a distinct personality and unique games suited to its hardware.