dang's biggest contribution is setting the example. You can see it in this very submission—his reactions to pretty severe criticism in the subthread above are universally calm and measured, even when the other party gets quite aggressive. And he's also quick to talk down people who think they're defending him and/or HN but are doing so in an aggressive way.
He's the same way when he's moderating, and I've definitely patterned my own pseudo-moderating comments after what I've seen him do.