[Marc]

Well, here's another instance that's easier to understand. Think of skidding down hill, as one often would do skiing moguls. Assuming that the skier isn't accelerating downhill, merely skidding down hill with constant velocity. To maintain a steady skidding velocity, the force of gravity pulling the skier down the hill must be balanced by the force of friction generated by the ski edge pushing the skier "up" the hill (in reality just acting against the direction of travel). Heavier skier means bigger force of gravity, which means he requires a bigger opposing frictional force. A bigger opposing frictional force can be accomplished by having more ski edge length in contact with the snow, i.e., a longer ski. Again, height never comes into play here.