So let me get this straight, you are attempting to prove your theory by pointing out a 2/3 people? Of which a few how some tremendous natural talents. The question was about the overall increase of a larger populations/group of runners and not a few people you try and use as examples. Thank God you don't control the future of American distance running as we would be in a much worse place.
As was stated earlier the move back to mileage and away from the lower mileage trend that caused us to send less than full squads has had a great impact on our slow rise. It isn't everything but it is a large piece of it.