The biggest reason that positive reinforcement training is so effective is that is uses rewards such as attention and or treats to teach the dog what is expected of it. When the dog performs the desired behavior, he is provided with a reward, most often in the form of food, but it could be a scratch behind the ears, a rub under the chin or a pat on the head as well. The important thing is that your dog is rewarded consistently for doing the right thing.
When understanding what makes the system of reward training so effective, some knowledge of human history and dogs is very helpful. The earliest dogs were most likely wolf pups that were tamed and used by early humans for protection from predators, as alarm systems and later for guarding and even herding livestock.
It is thought that the wolf pups which made the best companions were the most easily trained, or it is possible that these early dogs were orphaned or abandoned. Whatever their origin, there is little doubt that the vast variety of dogs we see today have their origin in the wolf.
A dog with a more submissive personality will be easier to train using positive reinforcement, he or she will not want to challenge the handler or trainer for leadership. There are very few dogs that do not respond well to positive reinforcement training.
Positive reinforcement is the best way to retrain a dog which has behavioral problems, especially one that may have been abused in the past. Getting the respect and trust of an abused dog is a very difficult task, and positive reinforcement is better than any other training method at creating this important bond.
It does not matter what type of dog you are working with, chances are it can be helped with the positive reinforcement training methods mentioned above. Be sure to base training methods on respect and trust, rather than intimidation and fear, this will be the most effective way to properly train your dog.