The 'epidemic' in obesity isn't just from a redefinition of the BMI. There's something going on in the U.S. that is drastically affecting the average weight; no one seems to know what it is*. For example, just look at newsreel footage of crowds from a couple of decades ago. It's amazing how thin people seem.
It's not just a matter of will power, either; statistically, diets don't work in the long run. The only thing that has been proven to get the weight off of very overweight people, and keep it off, is bariatric surgery. Not that there aren't exceptions (though even the exceptions tend to relapse after a couple of years), but statistically it takes surgery to keep weight off of someone with a tendency towards overweight.
That said, 'fat' does not necessarily equal 'out of shape.' A person's resting heart rate and B/P are much better indicators of their fitness level (and likelihood of dropping dead during training) than their appearance is.
*there are, of course, lots of theories: too much high fructose corn syrup, too much TV, fast food, etc.