This is what turned me into a winter commuter as well. I used to quit around Halloween and then go through the pain of trying to get back in shape in the spring, but a couple years ago when I totalled my car right around quitting time, I just said "well, at least I still have a bike" and discovered winter riding to be amazing.

I've also developed a phobia of being stuck in traffic jams, which are more common on bad weather days. Blowing past frustrated drivers is one of the great pleasures in life.