Apple has invested a lot in having the biggest brand value. Even though some other manufacturers have brought out arguably better hardware, some of which is quite innovative (e.g. the ASUS transformer), there's just no marketing going on. Without making a name for themselves, people won't recognise the other brands and when Apple steals the best ideas (as they always do), people will just think it's Apple being clever again.
Also, although you may not agree, the "it just works" mantra around which iOS is designed appeals to a lot of people. Android is different on every machine.