Not too surprising. The first 2 weeks of the price drop in November for MS were massive.
I know, but it's still December, a month with usually higer sales (also because there's one more week counted). Plus, it's not like December was deprived of great deals for the console: the insanest one (One AC bundle + Destiny + 50$ gift card for 349.99$) was for December, after all. Certainly, it's still a pretty good result, no question about it, but.