Google introduced new fraud measures (again)

What I want to know is why have they waited so long to hook up Adwords and Checkout. Instead of bidding on $x/click, someone who signed up for Checkout could instead sign up and bid on $x or y% per sale, effectively eliminating fraudulant clicks.

I guess the trouble with this is that you'd still be able to send a truckload of traffic at a competitor to decrease the Google cut per visitor. But it would totally eliminate people artifically increasing their Adsense clicks, and if they optimised for the Google income per Adsense view on a site by site basis, then the long tail would effectively be safe from people trying to decrease the rank of their competitors. Not to mention that the data from the long tail would give you an excellent idea of who is being hurt by artifical traffic (you could even use the data from the long tail to rank the main Google search ads which would eliminate the problem entirely, perhaps at the risk of a bit of inaccuracy).