If I had more a much stronger desire/willpower than George St. Pierre to excel at fighting, I would train harder than he did... and I would be a better fighter. The man is great because he's trained hard, worked out, etc.
Willpower may not be enough to make you a success on 30 seconds notice. But you can get better at almost anything over time by working at it.
Though I do agree that you can get better at things over time - in fact I advocate developing habits as a way of "improving" your ability to manage your behavior and augment your willpower.
Training like crazy - great. Physically gifted (fast-twitch muscles, size, reach etc.) - great. Those two factors build a great foundation.
But nothing replaces fight time. Until you've put yourself in competitive combat situations, there is no way for you to truly understand how to react naturally to a fight situation. Honing your fight craft and anticipation is the difference between victor and vanquished at the very top.
The exact mechanism by which one becomes good is really a tangent to the original article and my the comment you are responding to.