In my opinion, those two guys are doing something right pushing that kind of weight around. Once you start getting past the 500's on anything, you are one incredibly strong bastard. It would be very interesting to watch one of the two go through a training session one day. really incredible, I think. Freak strength like that, I think comes largely from genetics. Then, once steroids are added later, and practice w/ lifts, incredible things can be done.
Just my opinion though....