I feel like Google and Yahoo results are pretty comparable in terms of relevancy/quality--and have been for a few years now. Sometimes I get better results in Google, sometimes Yahoo. Well, according to the Compete blog Yahoo has a lot higher "search fulfillment" (meaning they find what they're looking for, or a least click through more on searches) than the other search engines. Too bad for Yahoo only 20% of the Internet population realize Yahoo's better.
Matt Cutts made the comment that more people use Google to find info that doesn't require a click through--and Google is better at providing info in a snippet so you don't have to click. Matt can't really argue with Compete's data, it's more like he's just caught up on the terminology. He's basically saying that just because people don't click through, doesn't mean they didn't "fulfill" their search query. Google doesn't need to defend itself on this issue--the fact is they have 70% of the market, so who cares if they get a slightly lower "fulfillment" ratio, or whatever you want to call it, they're still the king of search.