Surely the key to successful weight loss is a change in diet, COMBINED WITH regular exercise. It's that latter point that most people have trouble remembering.
The fact that this woman was using a Wii is purely incidental. She could have been using an exercise bike, going for a jog, or anything else as long as she was active. The Wii just got her off her arse.
The Wii didn't cause her to lose weight, her strong mind and will-power did that and I say good on her!