With Wii MotionPlus the game will no longer be dependent on IR. With MotionPlus it could help improve controls. IR is NOT perfect, for example, have you ever pointed a little too far to the left or right on a Wii FPS?? What happens? The game loses track of where you're actually pointing. This could be resolved with MotionPlus and let's be real here, aiming can be a little too sensitive.
Did you notice during the E3 conference the Nintendudes had to point at the screen and press A?? I'm hoping this is an auto-calibration feature that can finally rid FPS's of an aiming reticule/crosshair. If this is possible this would mean we'll be aiming with %100 accuracy.