Okay-- Mark (or Dottie, for that matter) can feel free to correct me here, but I'm going to offer an explanation as I'm (elsewhere) a message board administrator myself.
You're explaining what I could equally have explained myself, and I've also, many times, administered message boards. I'm sorry if I wasn't clear. Partly this was because I misunderstood the situation, thinking that it necessarily must have been done by an administrator.
What I do think is that it's legally (though IANAL) and morally unnecessary, and a really bad idea, for board administrators to provide (turn on, typically) an option that allows users to delete the post as well as its contents. The alternative you allude to, allowing people to edit a post however they like, is far more benign, as it alerts later readers to the fact that something was deleted, and prevents much confusion.
(While I'm pontificating, though, I also think it's asking for trouble to permit posts to be edited after they've been replied to
without the post being marked as edited. The moral is, always quote the post you're replying to, but I don't do this reliably myself.)
Whilst I completely take the point that there can be good reasons for deleting posts, I feel this is something that it's reasonable for a community to disapprove of as a general rule. Posting on a board is entering into a conversation, and there's a moral sense in which the ownership of the sense (or nonsense :-) in that conversation is shared, not sensibly partitionable between the participants. I for one would not stay here long if I started noticing often that people were deleting posts.
