I understand you I believe..
Google does'nt make money off of Android so to speak, It makes money off of Google Play Store... Normal Consumer's don't really see "Android" They never say "I have an Android phone" or even walk into a store to say "I want an android Phone".. They now walk in and say "I want either a Samsung Phone or iPhone".. OEM's are not really shouting that their phones run on Android anymore.. It's more or less their own brands.
If Sammy wanted to, they could ditch Google's Android OS, and just skin their own OS as the same (TouchWiz).. Not many people would notice, only problem? All their Google Play App's would disappear (but Samsung pushes their own appstore lately so meh)
Without the OEM's, Google wont be making money off the App Store, which is where they make their cash, and the data for Ad's. They don't make money if an OEM Sells their phone's with Android. (unlike Microsoft, which charges OEM's to use their OS)