Deleting whole threads might be a bit much, since once a thread it's not really owned by a single individual anymore, you know? (case in point, this one. Since I took the trouble to post in response, I would rather not waste my time with posting in the first place if someone is just going to come along and delete the thread because they started it, and were it the case, I might find myself more and more reluctant to participate under that constant "threat")
But I agree about individual posts. As it is, you *can edit a forum thread post to effectively delete, simply by replacing your content with a "...". As for updates though, a minor mistake is locked in place for all time with the current system. Can't even edit to fix a glaring typo, so at a minimum, it would be nice to be able to edit them as well.