Each key is used to encrypt a copyrighted Haiku written by Dr. Felten. This gives the key the "colour" of an access control device. Thus, if somebody else publishes your key it becomes a violation of the DMCA because the 128-bit number is a circumvention device. (At least according to one reasing of the AACS-LA's theory.)
Obviously there are a lot of holes in this story. We could patch things up by requiring user-submitted haikus, giving the encrypted form for storage, etc. The primary legal difference, however, is that the "colour" of the key is not a property of the key itself, it's a property of how you got the key. Nobody is publishing your favorite 09 etc key just because it's an answer to some interesting problem or because they generated it on their own. It's because of where the key came from. Really, AACS-LA is not (or at least should not be) making the claim that they own a particular number but that they own a particular piece of knowledge, and that the disallowed behavior is not publishing a number but of disclosing that knowledge.
... which is actually one of the things I find most odious about the DMCA; it comes very close to creating a thought crime in which mere ideas become "devices". I'm tempted to insert my usual rant about how the interior of one's mind ought to be involate but I need to get back to work.