Hmmm ... in my experience fighting click fraud, I got the impression that the buyers were dissatisfied with PPC, and wanted to pay fixed fees. But perhaps that's because relative to its competitors, they got virtually no conversions via the publisher. Perhaps PPC works well for a much more trafficked publisher. But this doesn't bode well for small publishers who want to sell via PPC.
Fair enough, but that's not a flaw in the methodology. I would expect that as the Internet matures as an advertising medium, it will be necessary for the ratings services to get more survey participants. Certainly, the advertisers will demand this, as they become more savvy about the value of their buys.
Anyway, thanks for your feedback. If anyone else knows of any technical work (even open-source work) along these lines, please let me know.
--gregbo