I think maybe the reason why it shows that there are a lot more headshots on that website that you're talking about is because the hitboxes in HALO 3 are off. I mean, I'm sure everyone has had this at one time or another where they shoot someone in the head, they see the blood come out, but the opponent doesn't die. I don't know if it's possible, but maybe that site tracks how many times someone actually gets hit in the head, but the game doesn't always register the kill. Just my two cents.