I'm referring to the verticals I know and about which I do ongoing research, which mostly aren't tech verticals. I've checked facts on those issues on Quora, which has been disappointing as a source of information on those subjects.
Well, without more information, I can't really prove you wrong ;-)
But I still contend that Quora has experts in more domains than HN does. Check out the breadth of industries represented on http://www.quoratop.com/. Of course, it's still tech heavy - but it's more diverse than HN.
It's not perfect - but it's a much better candidate than HN.
That list on Quoratop is dominated by tech bloggers and pundits. Not industry experts. Just a bunch of people with tons of followers and hours logged on Twitter and at conferences. When you can converse with core contributors to openbsd, openssh, and ffmpeg, the guy who wrote fucking bsdiff, and the creator of the first worm, that's really impressive.
As a sidenote, this is probably one of the biggest things I miss about HN's old days is how great the discussions were with such legends. The creator of Gmail & Adsense talking with you was a daily, awe-inspiring thing. Not that it doesn't happen still, but a lot of this old guard of commenters comment less and less with new vocal pipsqueaks filling up threads. Not that they don't bring value, but the old guard had a way with words that conveyed thoughts concisely.
But I think your argument stands, there are a lot of different and varied industries and interests represented on Quora. The only problem is that a lot of the questions and answers seem a little fake and dry. Everyone's got their name and reputations on the line, so there isn't much outside the usual rhetoric and repeated arguments. Though I will note once in awhile a gem appears from the trough.
The best sources for serious discussions online seem to have moved from Usenet newsgroups over to the pantheon of topic- or expertise- specific forums; Nuclear Phynance and Wilmott for quants and finance+banking, HN and a few other good forums for tech, CollegeConfidential for education, BodyBuilding for fitness and health, etc. And the huge constellation of niche, smaller forums. Then there are the generalist forums like Something Awful and lots of smaller ones with vague or whimsical/unrelated beginnings or purposes. IRC is still a great medium as well, but heavily tech-focused.
I think Reddit fills a hole here in a lot of areas, especially in the smaller and more focused subreddits.
Quora arguably has a marginally lower caliber of tech experts, but much higher for many other verticals including business, journalism, media, etc.