The fans in baseball can easily see the trajectory of the ball as it leaves the pitcher's hand at 90mph.  From this perspective, it is easier to see what the fastball's trajectory is like after a pitch.  One can determine that a 90mph fastball, if thrown consistently to the same spot, will arrive at home plate at a certain height.  However, a 95mph fastball will land in the catcher's mitt higher than the 90mph fastball.

Manuel Muñoz - Physics 212
Dr. David Newman
April 2011