Anti-trust laws.
That's the true answer.
Apple can sit back and do all their product integration - Apple Watch only works with iPhone, AirPlay only works with their devices, Apple Maps only works with Apple devices, AppleTV is and will be integrated in their ecosystem.... BECAUSE of Google.
If Google wasn't there with the overwhelming percentage of marketshare, Apple couldn't do all this. But because of Google, they can.
It's also interesting to note that if you decide to only make higher-priced items, thereby not being able to achieve the most marketshare, you won't be guilty of anything anti-trust. Apple is very smart in all this for NOT going to the lower end of the market. Apple products wouldn't be as good. The integration part is what makes Apple products better than the competition.