Every ground unit on a battlefield is amazingly vulnerable to attack from above. If guided with precision (and our weapons are nothing if not precise), there is literally no mobile ground unit available today that can withstand even a medium-sized (500-pound) direct hit. They are simply blown to pieces by such things, and again once the air defenses are destroyed there's nothing they can do to defend themselves against such an attack. On a battlefield in which your enemy has achieved air superiority if you move, you die. The problem is you must move in order to fight. Which is why even the fastest armored division is utterly helpless if the other side has free use of the skies.
When you hear of "massive formations of Iraqi armor", what you should immediately do is translate that into "giant defenseless targets". For a deeper understanding of air superiority than you'll get from the news, go read the whole thing.