Is there any reason? On BGG, you may edit them whenever you want.
Just misdid a post regarding the subject line and i am unable to correct it myself :(
I'd say BGG is the exception rather than the norm.
Generally, there's a short-limit on editing, so that people don't post 1 thing, everybody replies to it, then the OP gets edited, making the thread nonsensical for anyone arriving later.
See this FAQ.