I would agree with that. As a physician, I can see that. Something like 50% of medical residencies are held by physicians who graduated from foreign medical schools. I DO NOT mean to imply that foreign medical grads are not as good as American medical grads.
My point is simply that lots of bright kids who could be doctors choose not to go that route anymore. None of my doctor friends have kids who want or have gone into medicine. They actually limit the hours residents can work, which they never did for me "back in the day." My kids do say they want to be doctors (since I've brainwashed them) and they can "eat lunch with mommy at the hospital." I don't know obviously if they will really become doctors.
I think having a good work ethic is very important for gifted (and non-gifted) children. Otherwise, it's like having an expensive car in your driveway without an engine. It's not going to go anywhere.