FotoTomas makes a good point--bike cops cycle for different reasons than the rest of us. Most importantly, they cycle so that they can be closer to the people they are patrolling. Being on the sidewalk makes it easier for them to look into shop windows, and to keep an eye on pedestrians. I'm sure FotoTomas could come up with a longer list of examples.
As long as the bike cops go at a reasonable speed, they are perhaps the only type of cyclists who should be on the sidewalk.