I talk about this at the end of the post as well. I think a ratings panel approach doesn't apply well to the web because the web is so fragmented. (In a good way! I like that there are lots of independent sites!)
Unless you had something like 10% of real users or a super representative 1% I think you'd have a big problem with getting realistic numbers outside huge sites.
Maybe the web needs something like Nielsen ratings, where Verified real users voluntarily submit their browsing to help advertisers determine watch time.