If there's a killer app on their platform, then Apple can't change their platform in a way that breaks the app. Consider the hoops Microsoft has had to go throu

If there's a killer app on their platform, then Apple can't change their platform in a way that breaks the app. Consider the hoops Microsoft has had to go through with Windows and IE to avoid breaking important third-party products. Since the whole point of Apple products is high-end, uncompromising design, letting killer apps get the upper hand would quickly make iOS stagnate and lose relevance. Once that's happened, the only way to get ahead again is something like the MacOS-to-OS X upheaval, which wasn't particularly pretty.