Look at the statistics, and the percentage of the dog owners (Rotts, Pitbulls, Dobermans) are like. It's likely they are used for guarding, not family pets.
I know a family that own dobermans, and they always want attention, they're a bunch of attention-seekers.
None of them has bitten a person. They are very friendly.
It is how you treat and train a dog. Many pet owners make excuses for their dog's behaviours like saying, "Oh, how could my dog do such a thing" when it is actually their fault for not training the dog well enough. In most cases, irresponsibility take the crown.
No breed of dog is inherently vicious, and any dog is only as dangerous as the owner allows it to be.
Here's a website with a bit of useful information to it.
http://www.fataldogattacks.com/
http://www.fataldogattacks.com/statistics.html