Have you read Gladwell's book "Outliers"? Basically deals with the situational factors that create outliers like Bill Gates. Circumstances have incredible life-determining effect that go totally unnoticed too.
For me, it has everything to do with avoiding pain points on the consumers end. Keeping a consistant design/feel means Apple doesn't have to teach consumers new skills. Other platforms have to differentiate with size, shape, and OS. Each one requeres a transitional learning period.
Take siri for example. Apple is running a ton of celebrity ads just to show people how to use it, because siri is too different for the average person. Luckily for Apple, its just a feature, not the core product. Just like a new Android device, people will get used to siri eventually. The difference is the iPhone consistency makes the essential phone experience seamless.