Bitcointalk really just has one purpose now and theymos has one job, and that is to make sure satoshi's posts remain accessible and in tact.
You don't need a working forum for that, just archiving would be enough.
The forum's mission is (almost) unique on the internet:
the forum's mission to be as free as possible.
I don't know a single forum that offers the same level of freedom of speech as Bitcointalk.