Single caliper... 'Nuff said.
Besides, a few reviews said that the brakes faded very quickly. There are no miracles out there, it's either many pistons or you get slammed in reviews yet again. The fact that despite repeated criticism and the fact that ALL competition has VASTLY better brakes, BMW decided not to change them from the E46 speaks volumes about how BMW intends to position this car.
And all this "lightweight" bs and "lower center of gravity" when the car is heavier then the car it replaces (which uses no weight saving) and all this "born for the racetrack" spiel to impress the soccer moms and chearleaders with rich parents.
Think of motorcycles, every new model of a bike that comes out is lighter then the one preceeding it, while retaining all the amenities AND having more power. Why then bother with the CF roof if the rest of the package is so heavy? The new M3 is all about marketing.