I already wished for it in the past, but it would be difficult to incorporate with the current system, and there's the thing that all following posts would be deleted.
I suggested that you just be able to delete a post that hasn't been replied to yet, but if something so simple as that wouldn't be incorporated, I doubt this would be.
Anyways, I don't mind it that much, at least you don't have to suspect someone going back and editing-deleting their posts if you're arguing with them, or them doing a bunch of stupid crap and getting away with it because they deleted their posts in time. It gives them more incentive not to act like assholes.
Besides, Alex is likely much too busy to include something like that into the site, he's already doing the new look, and that's time consuming enough. He does have a life to work with, you know?