Why I Left Android for the iPhone

With Android there is an OS, and like Linux distributions there have risen up a number of distributions of android. Each device maker is able to use android for free to build a distribution for their phones, but it's up to the phone companies to maintain support and bring updates to their distribution. Because of this, different android phones at the same version in different distributions could be considered different OSes, and different android phones in the same distribution with different version numbers could be the same OS.

That's my understanding of it, and also why non-Google android phones often lag in support. It's all a numbers game and the phone companies make sure the best sellers get the fastest updates and get around to supporting the phones that aren't selling anymore when they have a chance