Those of us who ran track in high school or college will remember that track shoes presume that you are going to be up on the balls of your feet the entire time, even in the mile and two mile events. They virtually have no heel. Cross country shoes (5K in high school and 10K in college) are also built the same way. The surfaces involved would be cinder tracks, rubberized tracks, or golf courses. The runners involved would be young and fit, not old and overweight. Heel striking might be the result of running on pavement, or the nature of adult recreational runners, or a combination of both.