In my short time in EMS, more than once we have been not only first on the scene, but first on scene by a margin of nearly half an hour. The ground ambulance ride back to the nearest small, rural hospital is another story altogether - one example was a 2 hour ground ride to a hospital that could do little for the patient, compared to a 25 minute ride to a well equipped regional truama center.
The study, like all studies needs to have the parameters identified. In cities and urban areas, there is probably a good case to be made that helicopters aren't much faster.
Out in the sticks - there is no comparison.