i'm pretty sure this is called "planned obsolescence", and i'm pretty sure i learned that phrase from Yahtzee. it's when a company (i.e, nintendo) sends out a product they know is incomplete and then proceed to make millions and billions selling patches and appliances. it's a way to make money, and though nintendo is succeeding, it still pisses people off.
the latest VGcats comic explains nintendo's position pretty well. basically, hardcore nintendo gamers are royally fucked and will remain royally fucked. now old people and idiots have discovered nintendo, and since the normal person is so very likely to be far more wealthy than the hardcore fan (and far less concerned with the quality of a product), nintendo figured out that they would buy anything, thus leading to the wiizapper, the wiibalance-board, and now, the wiimotion-plus.
in short, it's a genius business maneuver, and nintendo is an asshat for making it.