>It was a little disheartening to see the number of Reddit-esque comments that are simply a couple of words along the lines of "omfg" and a constant stream of meme abuse. I expected better from the programming community.
You don't get good discussion from a commenting system. Github's comments aren't designed for with-each-other discussion, they're designed for at-the-author/audience commenting.
HN takes comment quality extremely seriously, and with-each-other discussion is perhaps the main focus.
reddit is somewhere in between: most of the users of reddit don't seem to be interested in discussion, but in open-ended polls a la AskReddit, IAMA, DAE, etc. The fact that reddit threads only last for a few hours, and that the volume of comments is so huge that it's hard to expect the people you're aiming your comment at to get anywhere, these both reward commenting rather than discussion; /r/bestof does as well. That said, reddit's topical breadth draws in lots of smart people, who are usually looking to talk about something interesting.
The vBulletin/phpBB model of forums doesn't really scale too well (unless you go the SomethingAwful route and impose a fee and lots of super-strict moderation) but it works well with up to around 150 active users. The best forums have the highest SnR on the Internet.
4chan-ish anonymity works up to around 5000 before you get chaos, hence the longing for "old /b/" and the value in the other boards.