It's not about how aggresive the breed is in general, it's about how much damage they can do when they go nuts.
And that is exactly why its unfair to single out any single breed. No one thinks about Golden Retrievers being dangerous, yet an elderly neighbor of mine was attacked and hospitalized and her dog torn open down the gut by two Goldens that had gotten out of their yard. Her dog did live, but not without several nights at the vet and a line of stitches from stem to stern. Nothing like coming home from work and seeing blood all over the sidewalk.
I am sorry about your wife. A neighborhood dog once charged my wife and dog while she was out walking and it still boils my blood to think about, so I know how you feel.
Unfortunately, we only hear about dog attacks on the news. No one reports the tens of thousands of Pit Bulls (or other "dangerous" dogs) that went through the day (or their life) without incident.