Having tried a Wii Sports exercise program, how much exercise one gets may depend on how much EFFORT one puts into it as well. I grant you, it's no gym workout, but this will get you breathing hard:
For 30 minutes a day I did:
1)15 minutes of boxing (moving feet, ducking, punching, continuously)
2) 10 minutes of baseball - but here's the kicker...I would shift my weight back and forth as I waited to bat (shuffle step), and as soon as I hit the ball, I ran the bases (in place) as hard as I could with my character. When pitching, I kept a shuffle step going as well.
3) Cooldown: either 5 minutes of bowling or golf. I would still move my feet, but much slower as I worked to earn an effective cool down.
Over a two week period, I lost two pounds. Wasn't much, but for myself, someone who's hardly ever exercised once since they forced me to take PE, it was a start. I moved on to better things (South beach diet, I've lost 25 pounds, and tennis). but at least the Wii showed me that if I chose things I liked, exercise could be fun. I know that's a really, really sad commentary on my life, but it is what it is.
Don't be too quick to rule it out; it may be again that it is what you make it. If you're going to be lazy and stand there and halfway do it, then no, you may not see benefits. If, however, you're going to work your behind off, there may be some benefit to it.