An interesting note from Bungie's Matt Soell at halo.bungie.org's forum, regarding Bungie's presence at MWSF in January:

This has very little to do with us (because we obviously want to attend) and quite a lot to do with IDG Expos (who put on the MacWorld shows and, judging by certain actions and policies, do not want us to attend the SF one).

Hmmm... at last, a reason for the much discussed absence of Bungie on MWSF roster. However, he goes on to say that we can still do our part to help out:

Those of you who are especially concerned, however, may wish to send an email to customer_service@macworldexpo.com noting that you sure would be disappointed if your favorite game companies were not represented at the Expo in sunny California this coming January.

Keep those letters polite, of course.