This used to be something I too wasn't happy with. But come to think of it, if we were able to delete our posts would it be fair enough? I mean we sometimes might be somewhat harsh, and we therefore might make some abusive posts which other users might take to heart and go report us.
Imagine someone got stuck in a similar situation and has made some unpleasant posts addressed to you, you've reported them, but before the admins came said person had deleted the posts - the admins will have no evidence to punish them. Oh, I'd forgotten - this place isn't moderated. So, whatever.