Lee2...
It really isn't easy to keep up with what happens on the field. There is no way one person can do it accurately. I watch our team sometimes and they're all in the zone doing what they do best. If they ever play FPS games, I never want to be playing against them.
I chuckle when I hear the ABC commentators ask the stat man for his numbers. They're close, but not right. Even then, things missed would be stuff like spoils, shepards, knock ons, and the detail of the stat as kick, can be long, short, backwards, along the ground... you get the idea. Simply put, the more people, good people, you have, the better the accuracy and the greater the detail.