Simple ssp, take me at my leanest I was 240 with 15% bf (not low but low enough for me as an endomorph). Thats 36pounds of fat. Remove that in its entirety (almost humanly impossible) and I have an average bmi(with 0 body fat). Sorry bmi does not take into account muscle period. It assume an average which in athletes does not exist. In order to make bmi more accurate they would have to take into account muscle mass and bone structure.
I don't care about statistical averages as I am not statistically average. Neither were most of my friends in football or basketball. We were all generally 'overweight' or 'mobidly (sp) obese' according to the bmi, when in fact we were mostly lean atheletes (with the odd football played being big)...on average it may work...but that isn't good enough. Most good doctors depending on your mass will either use it or not. My doctor back home refused to use it for the above reason, but was able to apply it to my gf.
So saying it is useless was maybe overkill, I just like to make sure people realize it is a very innacurate way to make sure you are normal. It would be interesting to see a study of bmi on strength and power athletes as well as another one on endurance athletes.