Icy roads are a problem, but studded tires would solve only one part of it - the one where I could slip and slide under a car or a bus. They would not solve the problem of other cars hitting or swiping me because they don't always have complete control. Roads here* are much narrower than in the USA - look at Smaug1's picture of the street above and imagine a two-lane two-way road, but only slightly wider than a single lane in that picture. European cars are smaller and roads are narrower, especially roads that were built many decades ago. And then there are no shoulders, not an inch, so I ride with traffic (right edge of the road). So, it is enough for a car to slide half a meter to the side (20in) and I am hitting whatever is on the right side of the road. Now, not all roads are so narrow, but most are and the ones I use to get to work definitely are. Whether I am commuting or just going for a ride out in the country, I always choose least important roads with least amount of traffic, which is always nice and more pleasant... but it also means poor maintenance, poor lighting and usually not even two lanes but just one where vehicles can pass each other only with lots of caution and at lower speeds.

So, there is a point - i.e. weather and road conditions - where I simply put my bicycle away and wait for better times. There is no point in taking big risks, especially when there is much more stress than fun in doing it.

* Smaug1, thanks for reminding me to enter location in my profile. When I registered two years ago, I wasn't sure if I would keep coming, so I gave only information that was necessary at that time.