Google had to release at least the core packages in Android regardless because it is based on top of Linux and the GPL license would require it.

But they open sourced much more than that, and under more permissive licenses.

The notable exception is of course the google play services, which is also strategic (they control the OEMs with this, among other things).

And the drivers, but that's mostly not them I think (they could possibly have required open source drivers though)

	▲	giancarlostoro 2 minutes ago \| parent [-]
		Embrace, Extend, Extinguish. Google did the Microsoft playbook. Look at email. Look at youtube we used to share videos via Kazaa and other p2p programs, zero censorship, all the same features (including chat!!) theres also XMPP which became Google Talk -> Chat -> Hangouts etc then the browser, how many random apps “Only works on Chrome” but you change the Firefox browser agent and it works there too!