IMO, we should close any threads that are older than 60 days with no replies. There are no direct rules against reviving old threads, but there is a thing called forum etiquette, and this is bad etiquette.
With those threads that you linked to, they must have been on the very last page (600 pages) of all the threads in that forum.
So, why would someone go to the last page and start replying? Maybe we should ask Diablo?
As for what do we do with the necroposters, I vote for the fire watch!
Dave