The mods on HN would kill a question like the following one, no doubt: http://www.quora.com/It-is-possible-to-drop-a-marshmallow-fr...
The discussion on the Tiger Mom stuff was much better on Quora than HN: http://www.quora.com/Parenting/Is-Amy-Chua-right-when-she-ex...
Hacker News is great at answering startup and coding-related questions, but none of you will be able to answer this one: http://www.quora.com/Hearing/Why-and-how-do-we-hear-ringing-...
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.
That doesn't mean it's "just" HN though. It's clearly aiming to be very different in the long term. At this point they're not really successful at being any one thing yet.