Technically "the forum" is many things, not really a domain, or database, or collection of BTC. I would consider the forum to be an entity mostly defined through trust and legitimacy, not that different from a polity. For the most part that trust is placed in theymos, so he's generally seen as the one in charge of the forum.

I guess on a technical level, I do own the bitcointalk.org domain, but I'm not involved in the day to day operation of the forum. Owning the domain doesn't come with any advantages on the forum itself though. I can't really come on here and boss people around, probably the most egregious thing I could do would be to just redirect the site elsewhere. And as others have pointed out, a domain change is not that big of a deal in the long term (though short term it's a mess).

I never really hear any feedback on this arrangement from anyone though, the little feedback I have got so far suggests people appreciate that multiple parties have differing levels of control over the forum. The forum is not my top priority since I focus more on bitcoin.org, so if anyone has the feeling they would prefer theymos being fully responsible for bitcointalk.org, it would be good to at least hear that opinion expressed.