I thinks it's a little weird. Denmark has cyclists all around as well, and cars. We're just taught not to open the door without checking for traffic (be it cars, bikes or pedestrians). You're taught that as a kid by your parents.

It's pretty obvious that when you park anywhere that's no a booth or your driveway you need to look before opening your door. I honestly don't understand that this is a problem. Do people else where constantly open their doors into traffic? Just "WHAM, door gets pulled off by a passing car". If you're not used to driving places with bikelanes I can maybe see it being a problem in the passanger side of the car.