This rule probably shouldn't be applied to higher ranks, though, as there are legitimate reasons why someone might want to delete many of their posts all at once (e.g. - participating in a thread that turns nasty).
Don't forget the legit bumps, that can only happen once every 24 hours, and requires deletion of the old bump. I have a few threads that I bump once in a while.
Meanwhile, working on the next thread

Each thread (after testing 4 of them) uses 35 Newbie accounts for bumpspam. That makes it quite obvious the same person is behind all of it.