A lot of companies use the calendar year for their fiscal year. If someone were being hit in a week from now, and knew they were going to keep getting hit ... or someone wasn't hit, but they can see it coming hard the next month and there after ... what a perfect time to close shop all nice and neatly but on December 31st, instead of opening up the books for '04 for just a few weeks or a couple months. (Not to mention why go to Vegas a few days later.)
I think that's the basis of the January Theory. At least that's the basis of it as I see it.