Simply, no. Instead, I still consider my iPhone to be a phone first, maybe a mobile web browser second, and a utility thirdly. I probably associate my iPhone with games and the very bottom of the list. But enough about me, can other people appropriately call the iPhone and iPod Touch a mobile gaming platform?
Certainly Apple would like us to "bestow" the iPhone OS as a gaming platform, but I don't think that the core gaming audience would agree to do that. I can see how those who have not been gaming for several years up until their iPhone purchase would want to call it a gaming platform, but ultimately we have to understand exactly what makes up the over 21,000 games available on the App Store.
Anyone with the ability to infer things about the App Store can tell you that a huge chunk of those 21,000 games are repeats, one-offs, and copies. The App Store has a huge problem with multiple apps being released that all accomplish the same thing. That's what the ratings system is supposed to help with: whittling down all of those repeat apps down to the cream of the crop.
In some ways, you can surmise the problems the App Store faces with it's strengths. With so many developers creating new applications, it's hard to imagine any one niche going without an App to fill its space, but with all of those developers come the copy-cats and crappy apps that wouldn't necessarily exist if there was a bit more of a hump to get over in order to start programming for the iPhone OS. While the App Store has probably revolutionized the way the major publishers and developers look at gaming at large, it will always be plagued with Apps that aren't exactly all there.
Would you trade the 3,680 title library the Nintendo DS has for the App Store's 21,178 games? I know I wouldn't, and that's even counting all of the Imagine: Babyz titles out there.