Of course, that covers a huge percentage of bicycle usage. I wear no helmet when commuting, but I'll wear a helmet in unusual conditions. Most cycling is done in fine weather in ordinary situations.
If you want bikes to be a serious thing for commutes, you need to be able to ride in all weathers that you have in your locality. Otherwise you're just taking the nice days for fun, but you still make it necessary to reserve the capacity for seats in public transit, or capacity for autos on road, on the days that are not nice.
Helmets are not just for "unusual" conditions. Wear helmet all the time when you ride, make a habit of it, and you'll not need to even think about it. Just like the seat belt in a car.
You're right, but that has more to do with the cyclist being a fair weather cyclist, than being in Berlin. If you're a serious all-weather, all-season cyclist, you wear a helmet. In Berlin, too.
