The AKC doesn't register APBT's because they wanted nothing to do with them. The history on them is a little confusing and the advocates like to exploit the confusion.
A good read about the registering organizations here:
http://dogs.about.com/cs/breedprofiles/a/pitbull_history.htm
Here is the mistake many dog owners make: They fail to understand that when their dog is outside their control, it has no master. If someone forgets to lock the gate and they get out, something is going to die a horrible death.
Animals are programmed by their breeding to be a certain way, and some of these guys are natural born killers. They see the old, the small, the young as prey when their master is not in control of them.