I'm not sure it's the study that some people are criticising so much as the calculator.
For example in my case, 73 kg, 50 years, resting heart rate = 40 which gives me...
Conservative Best Marathon Performance (Normal Glycogen Loading):
2:55:35
Aggressive Best Marathon Performance (Maximal Glycogen Loading):
2:00:27
I can change my weight to 80 kg, 100 kg or even 1000 kg and I still get the same results - it just tells me to eat more carbs!
Now admittedly, at a resting heart rate of 40 it does give a disclaimer about how "At your high level of aerobic fitness, you best marathon time may be limited by factors other than glycogen storage capacity", but my heart rate isn't the same each time I measure it and if I had of entered my resting heart rate as 41 or 42, I would have got no such warning, regardless of the weight used.
The time estimates seem to be purely based on age and resting heart rate.