People say this as if the entire (or majority) of Android's success rests with what they initially purchased. In my opinion it has very little to do with that and a lot more to do with the billions of dollars invested into developing, extending the platform, creating and supporting APIs, establishing contracts with OEMs, developing apps, etc etc. Android wasn't some magic thing that anyone that purchased it would have been sure to be successful. Just look at how well MS did with Nokia's purchase.

So yes, Google did purchase Android but Google didn't purchase their mobile success story by purchasing Android.