My friend just wrecked his G35 in the snow in North Carolina. Slid on ice at 10 mph into another car.
I think experience was the biggest factor in most people's wrecks, especially those pileups in the highways. They drove headlong into snow at 70 mph probably and didn't realize how quickly snow makes things slick. Snow is rain that doesn't drain off the road and doesn't get pumped out by the tires. If it's not blowing off the surface from wind, then it's slick.