I've been commuting year-round for a few years in Madison WI. Temps can get down to -15 F under normal conditions, and last year a freak "polar vortex" got us down to -27 F, the coldest I can remember. Oddly enough I was at home that week because my workplace closed and I was caring for a relative.
For me, it's an adventure. Folks do all sorts of weird things, for me, it's riding my bike in all weather. My commute is only 4 miles each way with minimal hills, and I dress pretty warm, so I'm not really in any grave danger even if I have to get off my bike and walk. Folks in the north work real jobs outdoors in much more extreme weather, and it's just a fact of life.
For heat, I slow down. For rain, I have rain gear, or I just risk getting wet.
This winter will be my first with a dedicated winter bike, but I've been using studded tires on my regular bikes. So far, I've really had no bike related problems.