It might not be literal glucose consumption, but the body figuring it has calories to spare to indulge in a pointless (for survival) lab exercise.
Yes, the blog poster states that the brain consumes .25 calories per minute. But we are more than just our brain. The brain is part of a complex system. And so we can reasonably ask if our willpower, or other mental measures, could be affected by non-brain parts of the system.
Of course the brain is affected by non-brain parts of the system. But my point is that, in order for glucose to "replenish" willpower, it should be the case that some task depleted glucose by some significant amount -- hence the need for replenishment.
Yes, and tests have shown that it's not just calories. A small non-food gift can have the same affects as glucose. I agree that glucose may be some sort of indicator to the body that it should engage in some tedious task, but it's not the cause.