I don't imagine it does. The userland is a whole different thing. But that doesn't mean that I (or Samsung or Amazon or Mozilla) can't make changes to the kernel in ways that aren't possible with iOS, or benefit from Google's improvements to e.g. Linux power management regardless of whether or not my device runs the Android userland.
I'm not sure this is due to the GPL either. Google distributes its patches to MySQL, for instance, despite them running MySQL on their own servers rather than distributing it in such a way that the GPL would force them to.
They didn't for a while, then maintaining their fork got to be enough of a pain in the backside that they realised that keeping with upstream was probably a good idea.
Pretty much this. GPL or no GPL, there's a maintenance burden when you maintain patches on software when upstream is releasing new code you want that doesn't contain your patches.
It seems like that is due to the GPL. If they could distribute a version of MySQL with sufficiently useful improvements under their own license then they could charge money for it and go into competition with Oracle. Since they can't do that they no longer derive that possible benefit from denying the improvements to others, so they have a greater incentive to contribute them even if not required to.
