I have run/moderated several Forums. The open setup of this forum causes a lot of the issues. The size of it also contributes. They could shut it down tight, but then it would basically die. These type forums pretty much operate on some core members that choose it for their primary forum, but the majority of the number of members are relatively non-participants when it comes to daily posting. In order to gain the new members that actually post you need a LOT of members coming and trying it out. Basically if you lock it down where a mod has to accept new member case by case the number of people that actually come back 1, 2 or 3 days later to see if they were accepted is less then 10% in my opinion. Also when you do that It slowly chokes the site to death. As the core members move on the other things or get busy in the off season the site loses content making it not as appealing to new members. FYI this is just my experience, but as stated before I have seen it happen many times.

On the larger sites I ran it was nothing to boot 70 spammers in an evening.

My hat is off to the mods here they do a good job.