Speaking of Google... Why do you think they still chose the S4 as the next Nexus model? Appeasement? Hope that people accidentally buy a Nexus S4 instead of a TouchWiz S4? Intuitively, it doesn't seem to make sense for either company.
I can't see any significant way that it is worse for Google for people to have their software rather than Samsung's.
Although neither S4 justifies the price jump from a cheap Nexus 4 for me.
And assuming some people want a high end "Nexus Experience" phone, Samsung gets more customers this way, than if Google went with HTC.
That's exactly why I think it is a bad idea :) Why drive the Android device market towards a monopoly? It ties both Google's business and Android's success to a single player.
Samsung - in-line with their conventional shot-gun "catch-all" product portfolio strategy.