Google might not be pleased when they realize the implications of Amazon's newest app update. Instead of Amazon relying on you to head to their webpage to download the Amazon App Store app, you've only to download the Amazon App from Google Play. The big deal here is not that Google forbids apps outside their own store - they certainly do not. The big deal here is App Updates. Google forbids that apps that come from the Google Play app store be updated through any other means than the Google Play app store itself.