Well, I think the issue is that the study was conducted in houses without gaming consoles and thus not involving gamers. No real requirement was given for the usage of these games.
As I see things households who don't have game systems probably don't have them at this point due to a lack of general interest, or doing other things. Unsurprisingly the people with the consoles inserted into their homes probably didn't radically alter their life styles. The kids probably played with it a bit, but kept right on doing whatever it was that caused them to look that way to begin with since it was their primary interest... or a requirement. A kid whose family doesn't have a console might very well be so poor that the kid has to spend time working, and work does not always mean a lot of exercise, sitting around minding a store or whatever doesn't nessicarly mean you do much. Heck in a decade or so of security work I was well on my way to my current obese state (from being in pretty good shape) just from stress and inactvity.
To really judge, you'd have to find kids who actually used these products regularly, and as intended, which means families with consoles, and kids who wanted those titles. Some kid who say wanted "Dance, Dance, Revolution" or whatever game is out there for this now and begged for it for six months, and does nothing but play it on the highest difficulties trying to beat his scores every waking moment is a far better example of someone who "plays the game".
Likewise fitness programs for a console, are like any other kind of fitness system, they require work and adherance to the program. They work as long as you stick with it. The console programs are basically the same as any other workout system, it works if you do it every day for the allotted time, and keep pushing yourself to go a little further and faster each time.