I agree that paying attention plays a huge role in safe driving but I also belive that putting on winter tires also plays a role in safety. Winter tires are proven to stop your car sooner, provides more grip and that you won't get stuck in snow as often (we Toronto citizens know that Miller has cut back on snow removal and hopes that Mother Nature does the job).
$800-$1500 (depending on the car) is a lot of money. In my case, I have a $1000 deductible on my insurance. My winter tires have prevented 3 accidents so far. They've more than paid themselves off. Even if that didn't matter, we all know this, driving is a privellage, not a right. If they mandate it, there is nothing you can do.
When a car has winter tires on and a driver behind the wheel with a winter driving mentality in mind (driving properly for winter conditions) and who actually clears the windows and vehicle of snow/ice... it makes the roads that much safer.