Once people get used to use their bike in the course of their daily routine, they're quite likely to continue using it in the winter.

I've gone through three Berlin winters now with going everywhere by bike. It's a one-time investment in some good clothing, mostly for hands, feet, and your head. After that, it can actually be a lot of fun to drive on fresh snow, or through the blizzard.

In my experience, cars become a lot more of a problem in winter: they're more likely not to see you because it's dark, and because rain and snow are terrible for your vision if you're behind a windshield. There are also fewer people on bikes, so they don't expect you and pay less attention. With snow, there's also a tendency for odd-shaped large pieces of ice to end up right in your path, i. e. slightly to the right of the cars' track.