I've never understood the reasoning behind this; but since someone just necro'd a thread I had opened in 2011 (link) and it was closed so I thought I'd ask.
Wouldn't it make more sense to only close the thread if it's no longer relevant precisely because of its age?
Eh. The guy who necroed it brought up some real life bullshit or something, so it sort of looked bad. And the people posting weren't exactly posting on topic. And that person who closed the thread clearly stated he didn't like necros.
*pulls out a cigarette* I'd have been the PVP moderator if it wasn't for Dwyane Wade.
But yeah, those guys weren't talking about how scrub your BG team was so it was better to close it then to keep letting people give random complaints.
If it's something that's still relevant, we don't actually care if it's necroed -- this includes things like "what are some experiences you've had in pugs" or "what's your favorite vanilla dungeon" or whatever.
If it's dependent on a particular patch or date, the necro ends up spreading false information or you end up with everyone coming in just to reply that the OP is wrong/outdated -- this is the case for things like specific stat/gear/strategy questions.
In that particular case, I actually think it might fall into the first category; I'll take a closer look and maybe reopen.