I just did a little research and the Staffordshire was origionally used in bull and bear baiting (?). That was outlawed in England in 1835 and the dog's were used to fight in pit's. They are a cross between a bulldog and terriers. My guess would be the power comes from the bulldog and the heart from the terriers.
When they were imported into the U.S., they were bred for use on farms and origionally used for just that purpose here. Of course fighting is popular so they became the pit dog's we think of today. In fact the "Amer Pit Bull Terrier" is a larger dog than the "Staffordshire Terrier".
It is not the dog that is bad, the dog that has been bred to have a specific temperment and a willingness to fight back. The thing that is bad is some of the hands these dog's fall into where the,,,,,,,,,,agressive trait's are brought out. The same traits could be brough out of the "Dachshund", or several others but they would not have the strength of the "Pit", which was origionally the Bull Dog crossed with the terriers. I believe that "Pit's" are the choice of bad people just because of their heart in fighting back and more importantly, their predictable temperment. You cannot say the same thing about the predictability of the German Shepard of the Doberman, either might turn on their master. The dogs used to guard highly sensivetive munitions dumps in Germany when I was there were German Shepards. The handlers wore heavy dog handler suit's. The Shepards and Dobermans are both a much more intimidating breed when you just stand there and look at them. If you were betting you could handle a dog in a fight, would you take on the 45 or 50 pound Pit or a 80 to 100 pound Shepard or Doberman? The Pit has more heart.
I think it's wrong to judge the breed because of what some people have done with it. One of the most famous Pit's in history was the one on the old T.V. series, "Our Gang", "Pete". He was everything a pit is supposed to be but nothing that it has been reported to be. NOBODY accused "Pete" of being a bad dog.