What we're talking about is the waist circumference and waist-to-hip ratio as a better means of deciding the risk of weight, and absolutely--it's been known for a very long time, actually, that it is a better measure of the risk of weight, because body mass index forgets things. It forgets about muscle mass, it forgets about bone density, it forgets about racial differences; as a consequence, it's a less reliable measure. Of course, that reliability is really only in question in the lighter range of body mass index. Once you exceed a certain level, it becomes fairly incontrovertible.
You mentioned activity and its role. I wouldn't mind commenting briefly on activity and the role. People consistently talk about how important activity is in burning calories, and it is absolutely true that without physical fitness, people are far more likely to regain weight they have lost. However, the actual calories burned through exercise is fairly minimal compared to the number of calories one could restrict from the diet through knowledge and teaching.
For instance, should a person want to lose a pound in one week through exercise alone, they would need to exercise an hour a day, very vigorously, seven days a week, and not one time that week have anything to eat as a reward for their exercise--so while it is certainly a player, I think it is the minor player in terms of weight management.