I have a cousin who's a vet and he along with a friend of mine who was immersed in rottweliers before you could buy them here in the states both believe that the purebreds are weaker although they can't put their finger on why!! I've owned Rotts going on a little over 20yrs. My first dogs were healthy as a horse as they say. the male and female I own now are both sickly although they show few outward signs to the unsuspecting. I might be dogged out at this point!!!!!
Howie...it seems to happen more when a particular breed becomes "popular" with the masses, and dogs are bred for the wrong reasons, tending to pass more of the genetic faults. As you well know, Rotts are not a breed everyone should own, like so many other breeds of dogs. The Germans, for some reason, tend to breed strong dogs, particularly the Shepherds and the Rotties...also the Dobies, but a person is going to pay some pretty good money for a German bred dog.