Re: Quick - call a sociologist
In forum software of yesteryear, posts are often editable for a short while so typos can be corrected. There is usually a flag that the post has been edited and sometimes a history. Other platforms allow editing at any time until the next post is made (at which point all previous posts in that thread become non-user-editable), or a combination of the two. Or edit whenever and so what - its just a forum board.
It seems odd that FB didn't take any notice of who people like to edit/maintain their posts on a public(ish) thread-based conversation model given all the prior history. Probably just because they didn't need to, so less work.