Standing up allows you a lot more freedom of movement if need be. If you' re sitting down and a deer doesn' t stop in the shooting lane you' re hoping he will, then what? Rotating your body for a sitting shot is pretty near impossible unless you' re a contortionist - which I don' t think many of us are.
Personally, I' ve shot all my deer while standing. I practice sitting shots just in case I get caught off guard and need to make one, but it' s not my shot of choice.
As for Chuck Adams - eh, he' s over rated. Read some of his books and you' ll get a better idea of a lot of the questionable shots he' s taken at animals over the years. All in the name of the quest for the " Super Slam"