I've been behind the scenes with 4x4wire.com since its inception, and I agree that allowing posters to edit has some downsides. You've covered most of them, but we came up against a situation (which I can't obviously divulge) where there was litigation threatened between users, and the original poster edited for content to avoid legal action. Definitely not a situation you want to be in, as a third party host. After that, we stuck with the time window editing, and it is now policy...
Allowing it in the pic thread might be advisable, when you consider that people sometimes change their hosting etc, and then you suddenly have a bunch of missing pics. But otherwise? Time window makes perfect sense, and may actually keep trouble to a minimum...
(edit: I'm just a newbie here, so I hope I'm not speaking out of turn in contributing in this thread...)
Current: 1997 Pajero Evolution no.581, 2013 Lancer Sportback, 2003 Montero
Not forgotten: 93 Pajero, 91 Pajero, 96 Evo4, 91 Galant AWD, 89 Montero, 89 Raider, 88 Raider...