Why shouldn't Google attempt to drive traffic to their own products? If I write two books, should I be able to recommend one in the other? How is this any different?
the analogy is more like that of a car manufacturer gaining 90% market share, designing the interface between it and its seats to be proprietary (and preventing other manufacturers from learning about it except through a business agreement with them), then getting into the seat business and making it clear that third-party seat manufacturers make inferior products.