Nobody NEEDS them. I simply suggest them for anyone concerned with winter driving. I spend alot of time and miles on mountain roads year round, so it just makes sense to me to have a winter set (the last 12 years in the midwest I didn't bother with them as there are no hills to slide off of, now that I know how good they work I would probably reverse that choice, but I got out ok...). As I have said before many times on my soap box, the difference between snowtires and not is remarkable when in bad conditions. I have also driven FWD and RWD vehicles in the snow with bald tires, its really all about not being retarded or getting hit by a retard. Denver and Boulder tend to get as much snow sometimes as the mountains due to some fancy weather phenomena.
Besides, having a set of winter tires is basically a one time investment, you always need rubber for your wheels! For even greater longevity you can add a full size spare of each and rotate them all! It seems like you are buying extra tires, but what, you just gonna buy summer tires even tho you live somwhere that has a winter? Don't worry truck owners accept this logic under no circumstances for the simple fact that they can pull me out of a ditch.