There are multiple functions for 'Police dogs', patrol, narcotics, explosives, search, cadaver and probably others.
Many dogs of various breeds can perform most of these functions EXCEPT patrol. Perhaps I should have clarified that it is in the area of patrol dogs that there are so few that can do the job.
A patrol dog needs to have the 'something special' that will allow it to carry through in a real fight with an enraged adult human male. This is no small feat.
For example, there is a break-in reported and the suspect may still be inside, but will not respond to instructions to make himself known. A decision is made to send a dog in. The dog needs to be able to enter a strange building, alone, searching but willing to fight. If the dog does find someone, maybe the bad guy is scared half to death and gives up, BUT he may be very willing to fight instead. If the suspect sprays the dog with pepper, clobbers it with a chair and kicks the dog halfway across the room, the dog needs to immediately leap back up with an attitude that says “cool--- let's rrrrruummmble!!!!!”
and bring the fight right back to the suspect. A dog that goes into a bark and hold because it doesn't want to fight could end up seriously injured by the bad guy, or could allow him to escape. The dog cannot be mentally affected or 'ruined' by the experience or else it will have problems next time it's sent after a bad guy.
That is just one example, but the bottom line is that a patrol dog needs to have the courage, fight drive, heart, guts, or whatever you want to call it, in order to actually fight a human. Without that 'something special' what ever you want to call it, a dog will give up or back down in a real fight. That drive is not something that can be trained into them, they need to be born with it. We can train and build confidence, bite, control, etc,. But we cannot train the dog to have that 'something special'.
A dog that barks at the door, growls at the mailman, held a burglar at bay, or even one that looks awesome on the sleeve isn't necessarily going to fight when the bad guy is trying to win for real.
Police do their best to select dogs that have that fight drive. I will readily admit that I am not talented or experienced enough to select a patrol dog. The guys who are will tell you that they see very few Dobermans that can do the job. Hopefully this will change with more knowledge in the Doberman community and increased emphasis on working abilities, especially the sport of Schutzhund.
Yes, as eminart stated it's a matter of percentages. There needs to be more breeders who pursue working ability in their litters. As long as folks keep pretending that the Doberman is fine as-is and just as good as it ever was, all because it looks like the same dog in WWII pictures, the breed will remain damaged. Some breeders are trying. As workingk9s stated- time will tell. Having OCD over balls or being hyperactive in general, can be typical of some working dogs, but it isn't a reliable indicator of fight drive. My personal opinion- and this is my unscientific opinion only- is that some of the OCD and hyperactivity comes from an over emphasis on prey drive when breeding