It's about user experience. And Apple's got that all wrapped up in a pretty little bow. Whereas none of their competitors do (HP came close, and we'll see about Ice Cream Sandwich but my educated guess is "probably not good enough for the average person").
I keep trying to figure out what people mean by iOS's user experience. I've got a transformer with the dock. Absolutely love it. Notifications are simple and unobtrusive. There is a back button that works.
I borrowed an iPad for a week and had to keep reminding myself NOT to throw it against the wall since it wasn't mine. At any point the damned thing needed to open a browser or map from one app the way back was not apparent and I ended up hitting the home button and needing to navigate back to where I was in the original app. In Honeycomb, I just hit the back button and I'm back. I guess if all you do is play Angry Birds it would seem pretty simple.
Don't take this as a flame. I'm really interested in why someone who uses both iOS and Android on a regular basis would say that iOS has a better user experience. I develop on and use both, but my personal iPod Touch is used for nothing more than a source of music on my alarm clock and in my Jeep. I dread using it for anything else.
And as an owner of the original Palm Pre I can certainly say that WebOS beats them both by a mile. Too bad the hardware was such shite and the limitations in the API were woeful.