I'm sorry, I don't buy the "it's all in how you train them" argument, at least not in totality. While I'm certain that training comes into play, keep in mind that "Pit Bull type" dogs have a long breeding history as fighting dogs. We can argue whether or not how precisely the "Pit Bull" breed can be determined but lets not forget their selective breeding for Bull Baiting and fighting.
"To understand the origin of the pit bull, one must go back two hundred years to a time when two dogs fighting to the death in an arena was as acceptable as two prize fighters punching each other in Las Vegas is today...
...the Bull Terrier was created "by crossing English Bulldogs with several breeds including Black and Tan Terriers, Spanish Pointers, English White Terriers, Dalmations, Greyhounds and Whippets in order to create a dog breed that would fight other dogs." (link)
Also, while acknowledging the limitations of breed identification, the Centers for Disease Control nonetheless has this to say:
"Despite these (breed identification) limitations and concerns, the data indicate that Rottweilers and pit bull-type dogs accounted for 67% of human DBRF (Dog Bite Related Fatalities) in the United States between 1997 and 1998. It is extremely unlikely that they accounted for anywhere near 60% of dogs in the United States during that same period and, thus, there appears to be a breed-specific problem with fatalities."
Nobody knows risk more than insurance companies. They study it with far greater precision than anyone else. That they would seek to disallow coverage based on breed profiles shows IMO that certain breed profiles are predisposed inflict injury and aggression. Keep in mind, most of the time these fatalities are kids (70%).