Well, it's been said for years that Google's biggest competition is not MSFT or Yahoo, it's Amazon. Put in that context, I think it makes sense. When I want to find the best price for a product I generally search two places: Amazon and the Google Products search. Doesn't make sense for Amazon to get a cut if Google doesn't.
It's because one day Amazon will be the only place anyone buys anything and thereby it becomes the only company that would need to buy ads, and in a monopsonistic auction the winning bid is zero.
Seriously. The less competition for ads the less money Google makes. Google has every reason to want a crowded marketplace and not a single 800lb gorilla as its only customer.
