Perpetuating the pit bull myth certainly doesn't help. Pits are obviously capable of causing great damage and death due to their power and drive (and tolerance to pain). But why do they attack?
First off, it is extremely important to understand that pit bulls were bred to fight. Part of that breeding, however, included a drive to only produce dogs that could be handled, that are "good with people". In the midst of a fight, they must not turn on the person. People are simply not aware of this trait, or choose to ignore it. This trait is as important as their fighting abilities.
When the pits were brought to the US in the later 1800's and 1900's, they were acknowledged as "nanny dogs": great dogs with kids. They were house dogs, family dogs due to their temperament and loyalty to their people.
This continued through the development of the American Pit Bull Terrier. This trait is still bred in the Staffordshire Terriers in Europe as well.
So again, why do they attack?
Breeding, pure and simple.
We knuckleheads have bred them for undesireable traits such as big blocky heads, size, and aggression. Backyard (in)breeders produce erratic and dangerous dogs - they do not necessarily look for the desireable breed traits, then these dogs go on to produce more of their kind.
I am not an apologist for the breed. I do love pits, I own one now and had another for 11.5 yrs. Part of being a responsible owner is understanding the breed. It's really painful to see these stories and the ensuing hype - but it is important to understand that people are causing the problem. If these dogs were inherently aggressive toward people, they simply would not exist in captivity. Stories like this should be used to end the bastardized breeding of unreliable dogs so we don't have more stories like this.
This story is a genuine tragedy and in no way should be minimized.