Its usually down to owners and way dog has been trained.
But...its surely beyond obvious that some breeds are inherently more dangerous than others...sometimes just because of size (I "fancy my chances" of fending off a unpleasant Chihuahua rather more than a Rottweiler), but also breed characteristics do vary.
I used to work for Post Office...and saw stats quite often on league tables for which type of dogs featured in attacks on Post men and women... some breeds featured more, year in, year out.
Some dog owners.... just can't accept there are problems with any dog. And most certainly think there's no problem with their particular dog. I do a lot of walking and hear the same old excuses trotted out many times, stuff like "He's just being playful..."
Of course...many years ago when we had a family dog..she was perfect...so I know I am no different to any dog owner when push comes to shove.