Actually I think the main difference is that Reddit is a business and HN is not. Reddit's management should do whatever it takes to maximise revenue, and this

Actually I think the main difference is that Reddit is a business and HN is not. Reddit's management should do whatever it takes to maximise revenue, and this often means going for the lowest (or at least lower) common denominator. HN is different, it is not directly about making money, but about getting intelligent people to have civil doscussions on tech and entrepreneurship, presumably to market ycombinator.