I don’t think it would necessarily have to be six bucks a month.
Something Awful is a one time fee of ten bucks (a few bucks more to get rid of ads).
I wouldn’t really mind a one-time fee for a lot of sites if it meant that they didn’t have to do a bunch of advertising bullshit,
Yes, but the Awful registration fee is more like a speedbump to make banned behavior at least a little expensive to the offending users. Most of the revenue comes from completely optional aesthetic purchases: avatars, avatars _for others_, smilies, etc. I suspect it's a whale based economy.