Speaking as someone who very casually uses an ipod touch, which I obtained on a special deal, and bought mainly because I just wanted to know what the device was like:
It's not easy to browse for apps or discover new ones. Sure, you can search, but search for what? I'm more likely to discover new apps when they're described on forums and bulletin boards than I am from cruising the Apple Store. Yeah, you can easily find the most popular ones in a list, but then, that's the point, isn't it? Once you're on that list, you're pretty much guaranteed to stay there, and remaining one of the small percent who gain the lion's percent of the income.
Well, I'm not wild about the device, anyway. Can't even simply transfer pictures to it without it reducing the resolution.