One company (Apple) chooses to restrict the hardware they let their app platform run on so they can have more control over the experience.
Comparing the use of one app platform to use of a competing app platform is a perfectly reasonable comparison.
There are many reasons. The primary one is that having the OS run on your own hardware allows you to have much tighter control over the user experience. After all, user experience is one area where iOS has always dominated Android.
I don't think that's true at all. As of ICS, Android is much better. Especially considering the horrible state of notifications on iOS and the siloed nature of apps. And usability took a serious hit in the move from iOS 6 to 7.
Next up will be some other metric that will be overcome like profitability, or total apps purchased or app store size or whatever. Apple has simply made a decision and stuck with it and the result is that it limits their share of the market over a more versatile platform.
Apple consciously refuses to decouple their hardware from their software (and I agree with you that the iOS experience is better than the Android one, although I don't think it's an objective truth).
Comparing iOS adoption to Android adoption is not some universally indicative metric (I'll bet all the money in my pockets that many more iPad owners know what "iOS" means than Android tablets know what "Android" means, which is incredibly important when you're, say, trying to build an ecosystem) but it is still important (I'm a developer with limited time resources! Do I spend X hours building an Android port?)
Of course it is.
http://www.extremetech.com/computing/167040-iphone-5-vs-gala...