> instead of a moderator it is the system).
That's actually pretty much the fairest solution there is: Threads won't get infinitely long but they get closed - at a time where most discussions are either over or profit from being carried into a new, fresh thread. Nobody gets to decide when a thread is over except for the few or many people who post in it and thus bring it to the "natural" end. The only "abuse" here would be people rushing to the end.
And if the thread gets closed/archived - big fucking, deal, make a new one, link the old ones, archive old threads offsite even if you must - all of these things happen on 2channel everyday and have, for years, and they work excellent. I see no reason why you'd call it bad.
Anyway, different boards, different atmospheres, different users, etc. I believe on some it would also be benefinitial to be able to close threads as a mod. Just because it's been abused on some boards we know doesn't mean it is a bad idea in general.