Well, I can't really speak for them, because I'm one of the lycra crowd who wears a helmet at all times. But my impression of mass "cyclism" in Copenhagen is that it's very low-key, everyday, a bit faster than walking, but more tailored to your needs than taking a bus. Regular city clothes, regular hairdo and make-up, practical but not very fast bikes, few conflicts with cars, fairly low speeds, low risk, for everybody who can turn a pair of pedals. So it's probably both a culture thing and a fashion thing, but also that type of cycling is just not that dangerous.