For those saying these deals are down to the retailer that may not be the case at all. In food and electronics many promotions and deals are in fact Vendor Funded - i.e. the vendor, in this case MS, pays for much if not all of the deal.
I'm not saying these are vendor funded, but I think it's likely they are. I see no reason why Walmart, Sainsburys, etc. would simply reduce their own margins significantly just on the 360 and not push PS3, etc. to a similar extent.
Personally, with the recent PS3 jump on the back of the price drop, and the YOY drop for 360, the 360 was the console that needed deals this December to remain competitive, particularly in US/UK.
Have major retailers by coincidence decided to offer the best deals in these countries on this console, or has MS decided to fund promotions to make sure it doesn't loose to much ground to PS3 this December?
I think probably the latter, myself. The timing, approach and scope of these deals implies to me they may be vendor funded. The PS3 would probably have less vendor funding as Sony have to watch the spending and, truth be told, right now the console doesn't need additional support from deals anyway, ditto the Wii.
Often vendor funded deals are kept fairly quite, with terms and conditions known only to senior staff at both the vendor and the retailer, so we may never know for sure unless someone has access at that level.
EDIT: just for those who always take these opionions wrong, I'm not saying MS is cheating or anything. Vendor funding is a common strategy that can be very effectively if carefully timed. If MS did fund these deals, I think it made the right move and the numbers show they will reap the rewards. If MS didn't fund these deals then by heck they're sure lucky all these retailers decided they wanted to heavily push the 360.