1) There is no karma system so there is no ranking based on quality. You can say that the number of likes can be considered as karma, but that does not rank comments or links.
2) Though people there can be considered civil, not all of the comments are particularly interesting. I come to HN as 80% of the conversations make me go "OMG, I never thought of it that way". That didn't happen here. But again I just looked at a small sample.
3) I don't care how many members you have, you may have 10 or 10,000 the question is, how many of them are actively contributing at least mediocre quality content. Judging by the profile pics I see, it cannot by more than 40 and that too is a conservative count.
About the rest, I really think that what happened and is happening with Italian Startup Scene can be an incredible case study (but we'll see what it's able reach). Facebook had a key role in this all, it acted as amplifier of each move.
When you submit something to HN, it is judged, no matter what. HN people are analytical and like to break things and analyse the system.
The level of Facebook addiction in this country is really scary. I see fellow engineers constantly on Facebook during free time, instead of actually building something.
Sad, really.
About 'building something', I can assure that it's the true spirit of the group, that's focused on doing things, much better than spending time to discuss ;)