Quora has an incredible array of people with domain expertise, many of whom are good writers who tend towards writing much longer answers than what you see on HN. I can't exactly pinpoint why the design of Quora prompts such a different array of questions and answers, beyond the different user base, but it's definitely not a fancy HN. It's trying to solve a different problem. If anything, it's a fancy cross between the Q&A-ness of Yahoo! Answers and a rabid, tight-knit fangirl community, but it's much better executed than Yahoo! Answers so far.
For instance, I'm afraid I can tell you an awful lot about tinnitus but I would be happier if I hadn't had the occasion to learn about it.