I couldn't even imagine how expensive those domains would be, epecially for pre-registrations as a lot of people would definitely fight for a bitcoin.tld domain.
Nah, .forum would still come around $50-$70 max. Of course, the bitcoin.forum name could attract a fair bit of attention; but, when bitcointalk.org has been operating as the "Bitcoin Forum", there's the priority. Same goes for bitcointalk.forum.
I don't know what theymos would possibly be doing with those domains though.
If only to block someone from squatting on that premium name. Newcomers might confuse one with the other, so best to stay safe by owning the domains that matter. That's what's done by the big ones like Google, Facebook, Apple, et al.