I know its been awhile because but I sent you a reference regarding glycogen storage and usage among various types of athletes overuse non athletes. The amount of glycogen stored in muscles is not static for all humans and depends to a great extent on the type of exercise you engage in.
I would agree that most people do not have to worry about depleting glycogen stores during exercise. However, you do not have to be a Marathon runner to blow through your glycogen stores in a single bout. Sprinters can do it easily through intense interval training. Its not so much blowing through reserves in a single session either. If you are not replenishing glycogen reserves adequately between sessions, you run into issues over multiple workouts.
These are challenges for low Carb athletes that Dr B acknowledges.