Wikipedia has a stated goal, a public management team engaged in discussion and debate with their users, and something resembling accountability. Reddit has the Silicon Valley's most notorious gender-baiting troll as it's head, virtually zero interactions between the corporate side and the unpaid community managers, and no clear rules on what it does and doesn't allow.

Honestly, the writing should have been obviously on the wall when r/jailbait was banned. I think they could have made up reasonings that would have placated the userbase, but they failed to, and they handled the resulting outrage very poorly. I was sorta surprised that wasn't reddit's 'digg moment', but I thought that the HDCP controversy was Digg's, so maybe I'm just ahead of the wave.