A-ha, so US sales figures are not the sales to the customers but to the dealers? Meaning in Jan 2008 BMW "sold" (= delivered) less cars to dealers, so the dealers pushed the leftovers from December - to clear the inventories? Kind a after-sale action.
Yet the BMW press release says something about huge demand for AWD models also affecting the figures - yet I guess BMW wasn't able to produce / ship them so quickly.
Hmmm ... Is it possible car companies sometimes push a bit more cars in December to the dealers, just to embellish the yearly car sales figures? IMO in 2007 BMW just wanted to exceed sales of 1.5 million units worldwide no matter what.
Btw, eg. EU sales figures are - in contrary to US figures - actually based on new car registration, which is done after the car is delivered to the customer. So EU "sales" numbers show delivery to customers more correctly.