Someone said:As mentioned, there's nothing forbidding you or the player to declare they are doing exactly that when they attack normally. It's like declaring they are aiming for the creture's vital points: you are always aiming for the vital points, there's no need to house rule called shots.
Well, the same could be said of "I wind up and make a powerful swing for maximum damage!" And yet Power Attack exists as a feat... one which a number of people have observed could be turned into a combat option, like fighting defensively.