The article was interesting but there were LOTS of things missing from it.
They do not mention the intensity of the workouts being done. a half an hour at a high intensity vs. an hour at a fairly low intensity could equal about the same amount of calories. This is why I'm always pushing the heart rate monitors. I can't tell you how many people I see at the gym who are on machines but are NOT WORKING OUT! They are just moving, if you can carry on a full conversation and are not breaking a sweat, you're not trying hard enough. Honestly, I could ride my bike every day for an hour and sight see, and go about 4 to 5 miles an hour, pedal pedal coast, pedal, pedal, coast... but instead I'm averaging about 14 miles an hour? The difference in calories burned is HUGE.
I can guarantee you that if I did two 15 minute high intensity workouts a day I'd burn more calories than one 30 minute moderate workout. The study even says that they couldn't get the women to do high intensity workouts. Also, if these women were supposed to do most of their exercise on just a treadmill for a year... yeah, guess what? unless you are constantly increasing your speed, the incline, etc, your body is going to get really used to that activity and you will need to workout for at least an hour.
I think for maintenance not weight loss, but maintenance if people were honest and truly exercised 30 minutes most days they could maintain. This article in my mind does nothing to refute that.