I don't seem to be able to edit a post I made a week ago to fix a bad link. It looks like the edit button disappears after some time. Why not always allow editing of a post by the poster?
The forum options I've seen are usually: never allow editing, allow editing within a certain time, allow editing until first reply, allow editing until first reply OR certain time, always allow editing. Same goes for deleting.
I haven't seen any problem from THIS crowd, but a lot of forums end up with some sort of flamewar or simple confusion, where someone says something, someone else responds, and mass hysteria when the first person changes their post radically after the fact. This usually takes the form of long threads of this sort: "Yeah, but before you edited your dumb post, you called me a pencilneck!" "Nuh uh, neener neener."
While I agree we're all mature enough, I don't see much problem with an update that says "oh, broken link, now it's http://foobar.qq/" - it can also help folks with google (who might be finding problems with broken link elsewhere) when you explicitly have a thread with broken link, mea culpa, and fixed link all together.
flamewars are thankfully absent from this forum so I doubt that is the reason.
Anyway, flamewar interactions usually happen pretty quickly, well within the time this forum allows modified postings so I doubt that would make a difference.
My guess is that the feature isn't there because nobody has asked for it.