There is a time limit of 45 minutes (???) after you post your original post where you can edit/delete it. Once past that time frame only a moderator can do this. If there are no major replies on your post we don't hesitate to delete it if you ask it to be deleted. If it has full blown drama circus of replies on it...then I don't think its fair to delete it since it then deletes and invalidates every ones response.
If it needs a simple edit that does't contradict or majorly change the content of you original post then a moderator will comply.
The idea behind this policy is that we want people to stand up to what they are saying and be accountable.