Winter tires are just another cost of owning a vehicle. With steel wheels, they cost $1,600 or so, and last 8 or 10 years. The all-season tires get fewer miles, so last longer, offsetting some of the cost.
My insurance co. gives a tiny discount. I am not sure they should be required, but if someone goes out in poor conditions and causes damage or bodily harm and haven't taken reasonable precautions, like winter tires, they should be held (ir)responsible.