It's surprisingly hard to match up movement speed to animation speed, either because the animation guy and the mechanics guy aren't best mates, or because designers like to tweak things after they've been made. Run aminations are easier to fiddle with, as the foot is in contact with the ground for a much shorter time and the body spends more time in the air. I guess that's why Mario et al have little legs and are pretty much in a full run at any speed.