Google does deals with manufacturers to include the nonfree Google apps with Android (Google Mail, Android Market, Google Maps, Google Navigation etc).
Any phone that includes these apps involves some kind of payment to Google and all Android phones I've seen include these apps.
Edit: More info Link
From what I can tell, that puts Google at a massive disadvantage. A carrier can replace those apps with free or in-house developed equivalents and then use the inclusion of those apps (which no doubt benefit Google in some way or they wouldn't have bothered making them) as leverage in whatever negotiations go on. It would be like AT&T being able to replace Apple's built-in mail program or Safari and then using that as a bargaining chip.
Further, I don't see how a license payment for those apps can possibly replace a steady revenue stream from ads, especially when you consider that Google is carrying the burden of the development costs for Android.