I don't see it the same way - Android's been behind the other smartphone operating systems in UI quality, and has had to iterate quickly in 2.x, 4.x and 5 in order to catch up. As they reach a point where Android has as good or better user interface as the competition (I think they're close to that now), the rate of change will most likely slow down.
Whilst true to some extent, it isn't as new as we think. Window Mobile has been around for a very very long time and Palm OS preceded it with usable Palm Pilot devices.
Although it's not obvious, I guess popularity as a lot to do with ergonomics and usability and their evolution so something will only continue to be pushed forward if there's enough people to actually use it. I don't know, I'm just thinking out loud why something which has been on the market for such a long time only recently has seen such a crazy amount of innovation.
