Well there's a key difference; Google doesn't exactly _need_ continued super-rapid user growth on Android. The reason slowing growth is a problem for Facebook

Well there's a key difference; Google doesn't exactly _need_ continued super-rapid user growth on Android. The reason slowing growth is a problem for Facebook is that it's the only way they could justify their valuation (or more importantly, grow their company), other than better monetization of users, which is their other Big Challenge. Also, the hypergrowth of Android is essentially driven just by the hypergrowth of mobile devices (since it's the most accessible OS for manufacturers and thus consumers across the world). The point of Android for Google was to foster this rapid growth of smartphone adoption without being under the thumb of a single vendor (especially one as capricious and overbearing as Apple). If it ever gets to the point that the world is saturated with smartphones, Google probably won't care that Android isn't the majority of that growth anymore.