Hah. Great argument. Especially when you consider that 'pit bulls' are not a breed, but an umbrella term for six breeds. So, yes, if you combine the bite statistics for six different breeds of dog (a few of which are very popular; all combined which make up about 7% of the dog population in the U.S.), the _six_ breeds will account for more biting incidents than any other _one_ dog. What a damning verdict.
This doesn't take into account any qualitative analysis either. For example, how many people buy a retriever or lab and train (aka, abuse) it to be aggressive towards everyone (i.e., a guard dog)?
Also, while voluntary, the American Temperament Test Society tests dogs in a number of scenarios for the overall temperament. Pit bull breeds do very well in these tests and have some of the highest sample sizes.
For example, page 1 (http://atts.org/breed-statistics/statistics-page1/#totals) lists the American Pit bull terrier and American Staffordshire terrier as ranking very highly and having 800+ subjects.