SonicRetro uses a heavily modded IPB, though, not a vanilla SMF. And the whole application/pending process has a nasty habit of making the place a bit elitist.
And it doesn't even do a good job keeping idiots out. Loudmouths like Kogen are allowed free opportunity to post all the stupid whiny crap they want, even though just about every word he says is wrong and mostly seems to be for the sake of starting arguments.
But the biggest reason they can get away with it there is that they've got quite a large active staff. I can think of at least three moderators, two admins, one "site staff", one wiki admin, and that's just off the top of my head; I'm almost positive there's considerably more that I forgot. I don't know how much say each of them has in moving people to trial member status, or approving them once they reach their 20 posts, but I'm sure they've enough that keeping up shouldn't be an issue. Compare to here, where the number of staff that's actually active is fairly low (Usually it's just sl, obesebear, Bosola, and me). Sure, we get fewer registrations, but it's FAR less likely that a staff member will be on at any given time.