At the moment, the racket's technology can identify the type of shot a player hits (forehand, backhand, serve), the kind of spin a player imparts on the ball and the power of a swing.
It's a rivalry defined by strength (Nadal's left-handed forehand) versus relative weakness (Federer's one-handed backhand), and Federer knows there's little point in hanging back and rallying with Nadal for hours.