I've always wondered how long it would take for HN to succumb to an eternal September where the "rest of the world" finally joins. Whatever HN is doing to keep discussions as high-quality as they are is pretty incredible. Yes, HN has changed over the years, but the fundamental aspect of conversation quality hasn't changed significantly.
The text only format is enough to keep 90% of people away.
Also the karma limits. I have almost 150 comment karma and still can't downvote. I'm not sure when downvoting/report, etc. come into play, but I'm fine even if it's much higher -- it seems to be working well.
>After users reach 501 Karma, they gain the ability to downvote another comment.
>If a user has 31 Karma, they can flag submissions.