The difference of course is that the highly gifted child can better "blend", by self choosing, by lack of challenge, by teacher choice, etc. It's less possible for the <70/60 child.
It's not often I get to disagree with you, Dottie, so I think I'd better take my opportunity.

My insight comes from classes and discussions with one of the country's preeminent experts on mental retardation and the law. His opinion (and therefore mine) is that people in the mild mental retardation range often "pass" as normal, usually by covering up with behavioral issues.
I believe that the statement we're evaluating is meant to compare the experience of a gifted child in the regular classroom with the experience of a ND child in a classroom for kids with MR. In both cases the child will be getting very little from the class. In both cases the child will know all or virtually all the material before it is taught. In both cases the excessive time spent on the material will mean that the child is bored out of his or her mind.
As far as advocacy is concerned, I agree that this statement could be inflammatory, and should be avoided. Perhaps it might work to say something like, "My child is working 3 grade levels ahead of her current class. Keeping my child in this classroom would be like putting one of her classmates in a class 3 grade levels below his abilities. That just doesn't make sense."