This is a great article on surviving situations like blizzards while you are in your vehicle. "Outdoor Survival: Spending a night in your vehicle" is a really good primer. The one thing that grabbed me when I read the first part of it was running out of fuel. Let me put this in the most simple terms - every time your vehicle's fuel gauge hits the 1/4 mark, fill it up.
Other than that, there are sometimes issues with snowplows striking vehicles that have been covered by so much snow the snowplow driver doesn't see the stranded vehicle. This is a very real concern and if you have the right gear, you might not even have to spend the night in the vehicle. I am sure the author of the article is writing it for the masses and what he puts forth is excellent advice for most people because most people are more likely to die outside of the vehicle.