[Ichthypresbyter]

And if you do want to lock your bike to something immovable, the standard seems to be a chain that locks into the ring lock, with a loop on the end- which gives you a lot more flexibility than a D-lock.

The other factor, though, is that standard Dutch city bikes are not designed to be easily dismantled. If you have quick release wheels, you want to be able to lock the front wheel as well as the frame (and ideally also the rear wheel).