Apple always gets the UI right - right enough to even overcome disabilities. This is amazing!
Many people don't need/want full-screen magnification/zoom all the time, just the ability to enlarge some text and tiny UI components. For things like that, I find linux far more accessible.
All of that said, most of my accessibility problems with Apple center around OS X.
Though you also can't enlarge text in iTunes/app store on the iPod/iPhone, the iPad has a much more usable 3-finger zoom, as well as a screen reader. The iOS touch interface is, as a whole, very intuitive and easy to use.
It is a bit too sensitive in some instances, but also rather forgiving in others. I'm guessing that has more to do with the app itself than iOS or the touch screen technology.