Mr. Obvious wrote:
This is a stupid rule, as it would put a 5' girl at 120 lbs. and a 7' guy at 168 lbs.
Agreed. Stray very far outside the normal height range for a U.S. male and the whole scheme fails. 5' 5" and 130 might be okay for some women, but it's a good 10-20 pounds heavier than most elites weigh.
People also have to understand the difference between looking at a graph of height vs. weight for elites and concluding on this basis what "ideal running weight" is, and looking at their own body and times and trying to mold it into a particular size and shape. Sure, most American elites at 5' 10" probably go about 135-140. But if you are 5' 10" and 160, like one 2:21 marathoner I know who is "boned out" at that weight, you may be able to starve yourself down to the "ideal" 140, but you will probably run far slower times.