I agree. Anyone who thinks a touchscreen-only device can replace tactile buttons on a gaming device is on crack. Although, the DS doesn't have a web browser built in except on the newer DSi, which is currently only available in Japan, and all web browsers on the DS/DSi have generally sucked for anything beyond text-only browsing. The homebrew browsers are actually somewhat better than commercial ones, although I don't have a DSi yet but from what I've seen the DSi's browser is still pretty slow. I wouldn't compare DS web browsing to the iPhone, but then I wouldn't compare iPhone gaming to the DS/PSP.
The biggest factor for me is the games, though, and only a Nintendo platform will ever have Nintendo games (industry trolls that keep calling for Nintendo to become a third-party developer notwithstanding). Nintendo is definitely one of the top game development houses out there, and Apple doesn't really have anything that can compete. Nintendo understands games, Apple does not.