[asid61]

I think that this closes the gap quite a bit. Although as stated, the tradoff for defense is that your alliance won't be able to get the third assist (20 points). Unless you can escape the robot you are defending, gain possession, then pass it off and return before the opposing alliance can pass to the defended, defense might just be removing two robots from the game.
Although because of the difficulty of shooting, defense on high shooters can be easily accomplished with a good drivetrain and a 4-5' tall robot.