Doesn't the article refer to people who actually have the "fat gene?" Not the population as a whole? I read it to mean that those w/ the fat gene need 3 -4 hours of moderate physical activity, not actual exercise to offset their genetic tendencies. Moderate physical activity includes any walking, housework, yardwork, baby and toddler care (lots of opportunities for functional weight training!!). Basically, I take to mean 3-4 hours of NOT SITTING, not 3-4 hours of Cathe!
Let's remember that Americans weren't overweight until the suburbs were invented. It's a sedentary lifestyle combined with oversized portions and unhealthy food choices that make most people overweight.
For weight loss for the average person, I've read that 1 hour of cardio is necessary daily, but it doesn't have to be grueling. Walking 4 mph would suffice. (This assumes that calories counts aren't too high.)