Google is the world's largest affiliate and the world's largest search arbitrageur, and they ban affiliates and search arbitrageurs all day long. This is so that they capture a larger portion of advertising spend and do not leak it people who they believe do not add value.
(Google is an affiliate: they do cost-per-action advertising on behalf of customers. Google is a search arbitrageur: they have a large source of searches which they can acquire cheaply, a large number of pages with content which is not quite responsive to user needs, and advertisers who are willing to pay for targeted traffic. The difference between Google and other search arbitrageurs is that typically the arbitrageur outsources the search engine and owns the content, where google owns the search engine and outsources the content to its AdSense partners.)
You can redefine anybody's business to look like he is competing with anyone else. The point is, those Bing and Yahoo ads still run on Google, so maybe there is some other reason for banning some affiliates, eh?
