Yeah, the problem is is that we should really hiking/climbing to pick food, be running around to catch food, spending the WHOLE day in physical exercise of some sort, whereas it is easy to go to the supermarket and sit down in front of the telly, or the, er computer.
For people who live in temperate to hot climates, track athletes actually represent what we should look like.
I am 6'4'' and 17 stone. My BMI says I am obese too. I used to do high intensity exercise and I went to 11 stone. I never felt better, but when I stopped, it slowly crept back up.