The moderation on HN helps retain civil community members as well. I've been thinking about moderation as a chicken-or-egg situation but maybe it's more of an equilibrium issue. I should go over my old slashdot comments and see if I remember what pushed me out.

Are you the davidw from reddit? Do you ever go on /r/portland? It's moderated to the max yet its still neither civil or engaging. Moderation matters but I think HN does a lot better due to the features that promote well thought out posts and don't really allow trolls to get much traction.