Winter tires have two significant flaws: they wear out very quickly, and they tend to be much noisier. The ratings (from Canadian Tire, e.g.) are not entirely (pun?) to be relied on, because they only test brand-new tires. An aggressive tread pattern will get much, much noisier after a year or two. And the wear rating depends on how you drive, your car's alignment being perfect, and the loads you carry. Realize that the cost of tires can be a significant part of car ownership.

That being said, winter tires (4 of them) are still worthwhile in terms of safety, BUT ONLY IF YOU DRIVE SANELY AND DEFENSIVELY. Observe that the owners of 4-wheel drive vehicles end up in the ditch a lot more than the rest of us; the reason for this seems to escape those drivers.