BRAND loyalty, FORCED or otherwise - call it what you want - the consumer knows what they will get with Apple, and these people want what Apple are offering.
You can call them all manner of names: iSheep, Mactards whatever (i'm not one of them BTW), but making the point about being 'locked-in' to a single device is not a major concern, nor an important factor to the consumer in general.
You make this mistake, by taking the tech-enthusiasts POV - a very small minority indeed.
The fact is, iOS is very good. It works slickly and smoothly, the hardware is very good (in general!) and the apps are plentiful and as good, if not better than Android equivalents. It also helps that iOS and Apple in general is consistent on all levels.
Android, on these terms is an almost complete fail. The thing is, this is what is important to the masses - not some silly fairy tale about 'openess' and the ideas of 'choice' that this suggests...