From what I can tell, Android exists so that Google isn't at the whim of Apple. The big G's greatest fear is that iPhones become the defacto smartphone, and Apple has the power to cut them out of their platform (by banning Google's ad networks and by setting the default search engine to Bing). I doubt the Android platform will ever really make money for Google.
As long as your mail app is a source of revenue for someone (whether from support contracts or ads), they benefit from you being locked in, at least locally. Globally they may suffer because of the loss of goodwill, of course.