I've asked a similar question about how some banned people still post. Look at the forum rules. Of course i would never break the rules. Now who wants a free iPod?
Most likely they've posted and been banned just a bit after.
Maybe a spammer posted a free ipod thread (who'd want ipods running loose anyway?), and then tried to help in another thread, and then got banned for the first one.
some members are banned and all their posts prior to being banned are left in place.
some members are banned and all their posts are deleted
but like Praetor said, after being banned they cannot post.