> HN is _not_ a monolithic bulletin board -- the messages on a BBS were never (AFAIK) sorted by 'popularity' and users didn't generally have the power to demote or flag posts.

I don't think the feature was that unknown. Per Wikipedia, the CDA passed in 1996 and Slashdot was created in 1997, and I doubt the latter's moderation/voting system was that unique.