I don't think they intend to imply that only the testmy.net results are valid, just that the method the Hughesnet corporate engineering group are using to diagnose problems has been calibrated to the testmy.net test with a very specific test setup.
This is just an attempt to eliminate as many variables as possible. As I understand it, the phone/chat folks are really just following a script and such tightly controlled tests would not be needed as they do not have access to the detailed performance data regarding the entire system that the corporate engineering group has.
