Idea is probably to ensure that relatively long delayed edits don't destroy the conversation flow of a thread. Editing really should be to cover the oops "can't spell", "incomprehensible phasing" or "finger trouble" issues. Real errors of fact, link or simple mis-understanding should be dealt with by a later posting recognising and correcting the error. Allowing much later edits could be considered as encouraging making yourself look clever with 20/20 hindsight.
Personally I don't see such as a problem. Folk here aren't that precious.
Hafta say I find it annoying to have spelling and finger trouble issues enshrined forever. Like starts for stops on a recent thread! Reckon there are more than a few folk who'd not mind excising a "humorous" comment that seemed OK at the time but embarrassingly less so a day or two later. Fair few instances where what would be fine spoken face to face comes over far too strongly in written form. Emotionally forums are close to mates chatting in the pub so its easy to overlook that its a written format whose style and content is best kept close to that of a letter. Whether formal or informal.
Clive.