...and you have a pretty reliable way of judging user-satisfaction...
User satisfaction of what? The hypothesis focuses on measuring the "quality" of the site. But user satisfaction also applies to Google's ability to understand the query. If you type Fishing Flies ito the search box and Google returns websites about flying fish, is the problem with the quality of the websites or the quality of the algorithm?
After the SERPs have been delivered, user satisfaction is a measurement of the quality of Google's algorithm. User satisfaction is not necessarily a measurement of the "quality" of a website. In the SERPs, I believe it's more a judgement on Google's ability.
There's a world of classification, statistical analysis of inbound links and outbound links, identifying non-spam sites and sites likely to be non-spam; by the time you get to the SERPs, it's less a matter of quality of the site and more about the usefulness of the results.
I'm not saying that spam sites don't slip through. They do. I'm simply suggesting that you consider the possibility that "user satisfaction" with the SERPs applies to a broader set of circumstances than just the "quality" of a site.