Hubb,
The aircraft are extensively tested with engines within a specific range, and then engine choices are made based upon that. The models are tested with engines well above what we are calling for, and the need for ballast, vibration, etc help us determine the desired range.

Believe me, excluding engines intentionally does no good for us, as it only decreases the marketability as you just described, so it is not done to be intentionally exclusive....it is done based upon the model's flight performance in the manner we have to assume an AVERAGE modeler will fly the aircraft (ie WFO dives, etc).