In terms of bodybuilding I think that nutritionists are very overtouted unless you are cutting and trying to maintain. Certain people perform better on certain foods and there's a million different variations that your diet can be.
Certain people digest certain foods and absorb nutrients from certain foods very well and others not so well.
The diet is tailored to meet your specific needs whether it is maintaining muscle and cutting fat or just bulking.
Only by trial and error will a person figure out what diet works optimal for them.
I think if I was one of these rich bb's I would have my feces checked after each meal to see what nutrients were actually used and what remains as waste.