Consider that most of us (yes?) earn $ from adsense. But first Google gets us those ads and from those sources we (web site owners) make our $.
Now move Google into a position of being THE knowledge source.
The only game changer is us. Google now gets all the money from their advertisers. No more sharing of the $ is required in order to keep the advertisers happy.
My guess on this is that this was the plan all along. But first Google had to use us as well as our visitors to prove themselves to the advertisers that they can deliver results.