I don't believe that, sitting on the side of the road waiting for a ambulance to show up is a whole lot slower then driving to the hospital, if you are 5min. out and it takes a ambulance 5min. to get to the scene you just delayed 5min., why not do a 30sec. stop and turn the guy loose to get on with his emergency?
I'm not turning anybody loose in that situation. If they were driving in a manner that catches my attention and gets me to pull them over, then I'd rather have an ambulance take them, than cutting them loose and "hoping" they don't hurt themselves or someone else enroute to the hospital.