Except nobody wants to post on a forum where they can get banned at a whim for something they didn't even know was against the rules, and people that run their forums like that are widely ridiculed (see: Tim Buckley)
But I don't think they'd run the forum like that. And mostly, I don't really have a problem with how they've moderated it in the past. But there's a big problem they're going to have to address sooner or later and that is the Dwarf Fortress community is continuing to grow, and it's already grown past the point where two people can really do any sort of proactive moderating in the sense that they read threads and enforce moderation outside of just responding to moderator reports, and nip problems in the bud before it gets to the point where someone has to get banned.
I'm sure they read some threads (the big ones on most forums like future of the fortress etc, the suggestion forum) but there are just too many forums and too many threads for two people to read them all, even if that was all they spent their day doing.
And I'm not just talking out of my ass here, either. We've experienced exactly the same thing in the bay12games IRC channel -we had to make the rules a lot less implied (basically before our rule was basically 'be chill' as well), and we had to take on more ops to deal with the growing size of the community. And we get a lot less of the flood of fans than the forums do.
Edit: unnecessary comma removed