[dvd3500]

As a forum mod/admin in other areas (I know, how could all not be slot cars, right) I think a better solution is that you can edit a post as long as no one has responded to that post.
If you say, answer a question during lunch (who needs food), get home, realize you forgot something and no one else has responded you can go back to edit.
If however someone has responded I don't think it is a good idea to be able to change the original post.

Concrete example:

I post a thread asking about the diameter of a wheel.
You respond and say "20 inches"
I go back and change my question to be about the length of a body part (an arm for example) ... the conversation, much like this post gets out of hand very quickly. (see what i did there? Thank goodness I have a day job...)

Seriously though, I have found that if someone responds you have to leave it set in stone. Otherwise the conversation falls apart.
in a face-to-face conversation you also can't "unsay" things (words are like bullets, you shoot 'em off and you can't call them back my Dad always said) .

Now I know there are rare occasions where something has to be removed but I would say those should be an exception...