This is a big claim with no justification.
Cars have dynamic traction control, internal temperature control, etc. You may get frost bite on your bicycle, but almost certainly not in your car. Having four wide wheels makes the vehicle radically more stable.
Add seat belts, air bags, etc. cars have far more safety features than a bike can.
Of course, cars go faster and going faster increases lethality at the limit. No argument there, far more people die in cars in general. But specifically concerning weather, cars allow people to do many things that a bicycle cannot.
Not to mention general comfort. Being in a bike in a snow storm is very unpleasant!
