I think all dog types are only as good as thier owners.
The media isn't interested in any good news about a dog who behaves.
They want to report on when a dog does bad (as a result of not being trained properly by the owner).
Bigger dogs do more damage when they attack or bite. When's the last time you saw a story about a chihuahua that had to be put down for mauling a 10 year old?
As a result bigger dogs who behave badly are what gets reported. It SEEMS to be a lot of Rotties, but again, the media picks and chooses which stories to run (sensationalize).