They measured calories burnt in the various games and found that, surprise, they didn't burn as many as if you did the exercise for real.
However the entire report rather misses the point: Wii Fit is not, and never has been intended as a competitor to real-life boxing, going to the gym, or going for a long run. Wii Fit's emphasis is much more on muscle tone, balance, flexibility, coordination and all over strength, than it is on cardio style fitness. While it has the cardio games like rhythm boxing, these are just a small part of Wii Fit's selection.
This misunderstanding is unsurprising really, the ACE is a trade group for fitness instructors, so naturally they are going to judge everything in relation to "traditional" western approaches to fitness. It's just a shame that so many people who should know better disparage something which people might actually enjoy, and want to do repeatedly rather than miserably pounding away on a treadmill.
Of course some might say they have a vested interest in seeing Wii Fit fail, but that would just be cynical
