I think there absolutely is a problem with certain breeds. I think it's probably a combination of ownership and genetics. Yes, all dogs can bite but I think a) there's a difference between a bite and a full-blown attack and b) most adults would stand a chance with the majority of dogs - not with these highly muscled breeds.
Lots of PP have made really good points and as a dog-lover, it's hard to find the right solution. But maybe the first step should be to bring in licensing - but only for the breeds that could be dangerous? So not just the Bully breeds, but also Rotties, Doberman, huskies, GSD, Akitas etc. Basically if you want a strong and powerful dog, you need to have a license.
Having so few dogs requiring licences should make it easier to enforce and eventually will cut down on the dickhead owners. It's the fatal and dangerous attacks that we need to focus attention on rather than this "all dogs bite" attitude which distracts from the clear problem.