That's true — I'd acknowledge that as a nice aspect of Android from a developer or enthusiast user point of view.
I believe that iOS would be less successful if it had similar capability, though. (I'm also the kind of person that doesn't really mind spending $100/year on a Dev account to install what I want.)
The point is that for the vast majority, and for developers looking to make a living, the play store can reject you. So for my purposes Google is pretty much in full control here.