HN is not a Q&A site, neither is Reddit. StackOvereflow is focussed on narrow topics (and moderated by Nazis). That leaves plenty of room for a site like Quora which is oriented around finding answers to questions you have on any serious topic. Other sites might have better matereial when you do a direct comparison, but that's like saying a book of essays by Richard Feynman is always more interesting than looking the same topic up in Encyclopedia Britannica.
That hardly seems necessary. Any generalized discussion site can answer Q&A, since that's just a discussion format. That isn't true the other way around, hence the StackOverflow nazis.
