Remember: Google does not want click fraud. Yes they share in the revenue, But it is detrimental. The goal of google is: Sell ads, sell the fact that google ads = profit for your site. In reality having insane click fraud is ok, as long as everyone is happy. Obviously people stop doing business with google if click fraud gets rampant.

The only question is: Is most click fraud happening on google, or other advertisers? This could be where google succeeds, "we have 10% of our competitor's click fraud, we are the trusted network"