We have people here that bike year round, even though our temperatures dip well below 0C (we get -25 to -30C on a regular basis, with windchill being -35C to -40C). That is far more effort than I'm willing to put in.

Once it snows, I consider it far too dangerous (though again, there are a few people here that bike in snow w/ studded tires). I only have a bike lane for a short part of my ride, the rest being on 50, 60, and 80kmh roads with no paved shoulder. I don't want to find out what happens if I hit a deep patch of snow, ice, or some cross-winds while a semi is passing me doing 80kmh.

As for your 2nd point, I made that mistake the first time it got close to freezing. By the time I made it to work, I had a tough time breathing.