As a guy who used to commute in Montana and N. Dakota, distance is really the biggest factor on winter commuting. I can ride 2-3 miles in all kinds of crazy stuff-- deep snow, blizzards, black ice, -70 F windchill.... but 15 miles is a really long ways in bad winter weather.

I've never had frostbite... but I have had some of my worst crashes when I was too cold or tired to really be riding safely. Nothing is worse than crashing on the ice after you're cold. And I didn't have a cell phone back then! Just dragged the bike and my sorry ass to the nearest store or farm house and ask to use the phone.