I think the difference is the amount of energy that you burn directly from the running and the amount of energy that you burn due to increased metabolism/repair

I think the difference is the amount of energy that you burn directly from the running and the amount of energy that you burn due to increased metabolism/repairing your body due to the exercise. The first is not going to be that different between people, but the second could possibly be quite variable. I spent a bit of time trying to find primary sources for the justification of these numbers and I couldn't find anything easily. I don't doubt they exist, but I've been burned enough times through sloppy interpretations of scientific papers that it probably makes sense to take a close look before I shoot off my mouth again ;-) I suppose either way, the original point stands -- it's incredibly easy to eat your way out of progress made with exercise.