Take 20 random 9-graders. Have them run only moderate amounts without any orthotic devices for 3-4 weeks. Those with near perfect biomechanics will remain uninjured while those who end up with shin splints, knee pain, ITBS, ankle pain, etc. will have some significant biomechanical deficiency. A common deficiency is flat feet. While every kid with flat feet may not end up injured, I don't think you're looking at the situation with open eyes if you don't think those with flat feet end up in the training room more often than those that don't have such deficiencies.
By the time runners get to college, they have had the chance to accomodate such deficiencies. So, if you're coaching at the college level I might agree that the injury rate, flat feet or not, might be similar among runners.
However, the average fit college male is not a runner with years of prior experience. Without the desire and inclination to overcome such physical hurdles, I don't see the average college male being able to train enough to run sub-7:00 pace.
The average kid that comes out for high school track/CC is not the average kid. Kids that hurt when they run usually don't bother to try running competitively - there are too many other options in life for them to bother.