No. Frame sizes tend to increase somewhat proportionally. So if you get a larger frame you get a longer top tube and a taller head tube. With H1/2/3, you can get a taller head tube without a longer top tube. The longer a rider's legs are in proportion to his torso, the more head tube length in proportion to the top tube is recommended. By having multiple geometries, Trek can fit more riders more effectively without sending long-legged riders off to comfort-bike land.