I live in Toronto and I cycle everyday in the winter and I have yet to use studs but that is going to change for this winter. Every year I take at least one big tumble and it is always on ice. The older I get the more it hurts when I hit the ground. Last year was the final year with knobby tires when I fell twice. I also met a guy who fell on the first icy day and broke his leg last year.
Of course we have Universal Health Care since we are Canadian, so that is taken care of. I even have great insurance at work, so I will get paid if I get hurt but I don't want to get hurt. I have broken my leg before, it's not fun and it hurts.
This year it will all change and I am getting studs. Since I cycle along the lake to downtown there is lots of freeze and refreeze which screams out for studs. Yes, commuting can be done with out them but if you cycle everyday and don't want to take chances, buy the studs.