I agree 100%!
In the 1:1 world, it's actually pretty rare for one person to be expected to do all the work himself (engine, interior/upholstery, body work and paint, etc.) In the 1:1 world those are all very different aspects of building a car that require very different and specialized skills and knowledge. In the 1:1 world it's generally understood that the vehicle itself, not necessarily the owner, won the award.
But in the model car world, the assumption is that we are judging one single person's skill at building a model car, and we assume that all parts of the model were done by the entrant. In the model car world, the model may be judged the "winner"... but what is actually being judged is the builder's skill, and the trophy is actually awarded to the builder of the model more than the model itself. The model is entered as an example of the builder's skill, while in the 1:1 world it's more the car itself that is judged... the assumption being that more often than not, more than one person had a hand in creating it.