As to the logic of corrections:

The poster can always make a new reply with the correction.
The poster can always make a reply by reposting the whole post corrected and edited.
I think the forums should freely record what we thought of typing at the moment.

If after a few hours you think you posted something your secret police of your communist country will be offended, then maybe you can ask a moderator to erase your post?  This doesn't happen very often.

I also agree on the 8 hour edit policy... I would even say more than 8 hours. the reason for this being that sometimes you come back next day and realize a mistake...

If people use the quotation function when replying to each others posts then it won't cause any confusion if a post that has already received replies is edited.