So just a few points:
BMWs are designed and (some) built in Germany, where last time I checked, it snows a lot, so I'd bet having RWD is not that big of an issue and the BMW engineers keep in mind that they have to get to work when it snows...
Second BMWs are designed with near 50/50 weight balance, which is ideal for snow driving as the car will behave neutral in low traction situations, rather than want to swap ends like a heavily-biased front or rear weighted car will.
Third, it's been my experience that a RWD BMW with winter tires is all but unstoppable in snow (if there's not so much of it that it is above the vehicles ground clearance).
Get yourself a set of winter tires on separate wheels and swap when the season changes.