For the time being, the standard for discussion on HN just tends to be better. Not "civil" or inoffensive, but more in that discussion seems to be the focus. The idea of "on topic" or at least "good" discussion seems well understood by commenters, and most of the time it seems like people are okay with either posting specifically to the topic or thread at hand, or they're happy just not commenting and simply voting.

The very idea that people collect here to talk about a topic at hand means that it's keeps the conversation a bit higher than elsewhere. I don't think I've ever seen people here push their number of upvotes as something that mattered. There is a lot of buy-in from users to ignore joke comments, even if they're on-topic jokes. How the community became like this I can't say since I have only been here about half a year/year I think, but it's a refreshing change of pace when you just want to discuss something.