Not only has there "been a 100 percent increase in patients complaining of Wii-itis," according to Dr. Dev Mukerjee of Broomfield Hospital, Essex, UK—a symptom that's never really described, but apparently caused by "sudden movements, resulting in tendon stretching or tearing"—the Wii could cause lifelong injuries. "It's possible Wii-itis may lead to rheumatism or arthritis later in life. Patients often have inflamation [sic] of the shoulder or wrist," says Dr. Mukerjee.
And let's not forget Wii-knee, which results from.... "the bending of the knee from the Wii-Fit game."
God forbid you actually move or bend your knees people. If anything, these people should be moving more, and then the generally mild activity induced by the Wii would not strain their criminally underused joints. Now they have the perfect excuse to be fat and lazy forever.
So, remember all this if you're thinking about picking one up for your parents for Christmas. It's not too late to take it back.