For what it's worth, if I post something that's later found to be incorrect or otherwise useless but has already been responded to by someone else, I'll go back and use the strikethrough format on the text in the original post and note why I did that instead of deleting it.
I have a habit of editing after posting as well, but I like the ability to go back and do that without a time limit, especially if I'm maintaining a thread that's meant to be a source of reference material such as a blog thread. I forget which forum I'm a member of that does have a time limit of a couple of days, and I've been annoyed by that more than once.