Just checked the box, next to the picture of nunchuk it mentions that a sensor bar is required. Just had a thought, when you choose which player is on pad or wiimote you need to point at the screen!
The sensor bar is only required for pointing at the screen with Wii remotes that are not motion plus. At least that is my understanding. You can aim at the screen with the side of the Gamepad, which only has infrared on the top of the controller, so the pointer on screen must be determined by the position and angle of the controller. Nintendo land makes no mention of requiring a sensor bar on the packaging either. Only that you need motion plus for the two games that require you to point at the screen at all.