Forums aren’t all like that, as the HN comment section demonstrates. While not a full-featured forum, it would be prone to the same effects.

Of course not all forums are like that, "only" the vast majority of it is. Even niche-forums suffered from this (or especially they suffered from it). I would not count Hacker News as a forum though. There is no reputation here, no visible karma unless you explicitly click on a profile, no avatar, no signature, etc.