I think you read me backwards. What I meant was that stackoverflow (and all the other stacks) are missing, and I find Quora seriously lacking, so the fact that it is on there at all makes me question the quality bar for the entire list.
I was thinking the same thing...Yahoo Answers? Give me a break! Im an ex-stackexchange 1.0 user/admin, and I love the SE Network. It should be number one on that list. Edit: the list is good, but he clearly should not exclude the other options, open-source alternatives.