Ok, stick with me on this one, the ukc is a business first and foremost, the reason your dogs are registered as apbt's with that business is because businesses need to make money and you want your dog registered, the ukc does not have an Ambully category, so they register them as apbt's. It's real simple, but causes alot of confusion (obviously).
The reason they are good fighting dogs is the same as the reason a red bone is a good coon hunting hound, because they have been bred to have the instinctive will to do so for hundreds of years. Do they like their owners possitive reinforcement? Of course they do, because they are dogs, but "pleasing their owners" does not explain why I have had to seperate litters of apbt's before 12 weeks old because they were hurting each other fighting with no "egging on" from me.