(Written, but not posted, before mention of the Facebook place. I believe there are people here who might use Facebook, but I've not succumbed to that fad yet.)
It's the logical place for one to be. We have a ToadyOne actively posting here and while other places might well act as a "come and look at this, %randomonlineperson%, there's a thing called Dwarf Fortress, and there's maybe even a few of us here on %randomonlineforum% who can chat about it, get you interested, informed and eventually hooked" but like I wouldn't expect there to be too much technical/IC Nationstates chatter outside of the official Nationstates board, etc, the natural place for the core community of DF is here, everything else is just aforementioned gossip/bait/nerdgasming with an eye to putting it out there to various different other communities. It'd make no sense (whilst bay12forums in still existence) to make a full community hub on a Minecraft forum, or on usenet:comp.text.tex, or on Weibo.
Which is not to say that there aren't some subfora on places dedicated to Foo within which Fans Of Foo And Dorfs chat away, and if you're significantly a Fan Of Foo yourself then that's a community you can appreciate. And some massive-appeal games without an 'official' hub (or with lack of fan-friendliness, for one reason or another) might have one or more off-shoot communities spring up. And as some people seem to like a facetimey/IRCy social network which bay12 doesn't give, then maybe facetimey/IRCy Fans of DF have been set up (sounds like they have), whether or not they have attracted The Creator to their fold, etc.