In my experience, much of the problems with moderation in other forums has to do with actual or perceived petty power struggles. If the mods are volunteers, there's a whole power struggle dynamic going on; if the mods are employees, there's a whole "rage against The Man" dynamic going on. Many forums have both.
In the case here, Toady is running a forum he personally owns, focused on a game he personally develops, and he's self-employed and answers neither to sponsors nor to publishers. He has all the power, end of story, no drama.
Since the game is free and the forum is optional, there's no reason he can't just ban people who are being a problem; it's free of the whole "people who think they are Internet lawyers who are owed something" problem.
Additionally, with personal moderation, everyone is aware that any time he has to spend moderating the forums is time not spent coding improvements to DF. The vast majority of folks who are here would consider that a problem. so the sort of "just dicking around to waste the mod's time" stuff you see elsewhere is comparatively rare (thank goodness). There's some interesting research on social compacts out there; one of the key lessons is that social compacts are more powerful than economic ones, but very fragile. See
this article about day care late fees for one take on one famous study. In short, i have an uncomfortable suspicion that if the DF forums ever got to the point they were too large and complex for Toady to moderate personally, they would fairly rapidly spiral into more problematic behavior requiring even more (and more controversial) moderation.
Or, to look at it another way, enlightened dictatorship is extremely efficient. The "enlightened" part is the hard bit.