Most people that want to post on Elitist Jerks are fairly well behaved and well informed people to begin with (Why else would they visit the EJ forum in the first place?)
If you think this you've probably never read The Banhammer (the forum on EJ where infractions are posted) or The Thread of Ultimate Suck (where bad posts are moved, usually after receiving said infraction).
in the meantime the official forums have to handle what must be 100 times the volume with a much lower average post quality even before moderation. Just saying "Well get more moderators then!!!" probably doesn't scale well to that sort of post volume.
Moderating forums scales fairly well with more people. A major problem with the official Blizzard forums is how much you have to do before you get banned. A much harsher policy would clean the forums up tremendously. Or so I'd like to think anyways.