The Nexus line is the best smartphone bargain that has ever happened, period, and it's still outsold by the Galaxy S III. They even use the words "pure google" in some of their marketing materials for the devices. Developers seem to be most of their market, though.
They could also opt not to include the Google properties on such phones (GMail, Google Play Store, etc...) but they don't. I suspect that relationships with headset manufacturers is the reason for this, but that's pure conjecture.