The distance from the turn around to the end of the trail is probably another 150-200 ft. The trail itself stops right at the train tracks a few hundred feet away from the summit signs. (There are actually two on either side of the summit house). To go from the turnaround to the actual top of the hill (which are not at the signs, those are 5-10' or so below the true summit spot), you have another 65ft or so of elevation gain and over a quarter mile or so of trail/parking. So a few orders of magnitude longer than the estimated 10-20 ft.
I don't know what the historical reasons were for the current day placement of the turnaround, but I'm sure that the fact that if you tried to run the race all the way to the top would run (pun intended) into the problem of what to do when the train tries to pass and blocks the course a half dozen so times during the morning.
Next time, if you want to spend the extra 10-15 minutes for the round trip to get to the true top, just tell them that you really, really need to go to the bathroom... :-)