That's because it isn't true.
Is there a breed of dog that can actually deal with an agressive pit bull attack?
My Wolf/Malamute/Shepherd ate more than one dog- including a pit bull. The pit bull didn't even tear him up that bad. (though a Rot did, as did other Malamute/Huskies).
And I guess this proves that lions aren’t so aggressive and imposible to control:
http://www.youtube.com/watch?v=bicIwwQhNtc