Well there's a classic example of one extreme end of the spectrum being stated as if it "should" apply to everyone...
It is science. You may be different, but not that different. All of our bodies function the exact same way with respect the way that we burn fuel unless we have a physical abnormality of some sort. My wife is a type 1 diabetic and it even holds true for her, though diabetes is thought to impact glycogen use when exercising.
The statement that we are all an experiment of one is only true to a point - in determining how to get the most out of our bodies or avoid injuries. But there are some absolute facts. Here are a few related to the current discussion:
* A normal runner's body stores about 3000 calories worth of glycogen in muscle and liver tissue. About 15g/kg of body mass * 4 calories/g.
* In addition to glycogen, we also begin burning fat for fuel while running long distances - the ratio can reach 60% fat:carb burn for efficient runners who stay within the correct zone.
* The average runner burns about 110 calories for every mile run or walked
* The above means that the average person burns less than 3000 calories while running a marathon. Even if you add another 1000 calories for normal metabolic processes, you only reach 4000 calories.
* The above also means that you will not run out of fuel when running even full marathon unless there is something wrong with your body or you have entered the race with depleted glycogen stores
Fact - people eat too much when they run, believing that it is necessary because they feel tired during/after a run. They feel tired for different reasons, not because of carb/glycogen depletion unless they have run very long distances. That doesn't mean that you can't or shouldn't eat anything during a race - just that you don't
need to do so if you have properly trained for said race. And part of that training should be running without fuel so your body learns to burn fat more efficiently. If you refuse to do this you will need to keep eating while running - but it is absolutely a crutch that you can teach your body to need less and less.
We can get into discussions about the "wall" and its causes, but most physiologists no longer believe that the wall has anything to do with glycogen stores (again, except where runners enter a race with depleted glycogen stores). They now believe that it is caused by racing at a pace higher than that supported by training.
We are all different, but not that different. We are all capable of so much more than most believe, but we have to let our bodies function as they were designed. To get the most out of our bodies we have to push ourselves - make ourselves uncomfortable at times.