I think that a lot of the unnecessary calls are a direct result of the US problem of "Sue the Bastards!". The medics at the scene are under a lot of pressure to make sure that the correct transport decision is made. Woe to the agency that elects to ground transport a possible C-spine or internal injury only to find out that they increased the severity of the injury or that the patient expired when a "higher level of care" or a "more rapid mode of transport" was available. Also, I doubt that the study took into consideration which hospital was on bypass. I wonder if they ever looked into the patients that were not transported by air and the outcome of those patients.