Anyone spent a winter in Berlin? It's incredibly cold. Traveling around the city on bicycle, train etc is great during the pleasant summer months but it's literally painful during the winter.
I live in a city that gets much colder than that in the winters, but still has plenty of bicyclists year round. It's all a matter of perspective.
Certainly getting around on the u-bahn was perfectly comfortable and the s-bahn was fine too.
Really didn't mind it much at all.