Jgalar, you're right about intelligence and artillery. In the intelligence arena, of course, there are the famous stories about the Navajo "Code Talkers" (NOT "Wind Talkers" as they were depicted in the movie of the same name). They simply spoke their native tongue and the Germans could not decipher it (because it's not a written language). There were also many successful deception campaigns. Ever seen the movie "The Longest Day?" It has the best Hollyweird depiction of the deception campaign at Normandy that I've ever seen. There were others, too.
In terms of artillery, I fear, we were superior only due to numbers, just like with armor.
As far as air power is concerned, we were again at a disadvantage in terms of technology. The German aircraft were more durable and manueverable than ours, and consistently defeated our pilots in one-on-one encounters. In 1944 they introduced the first jet-powered fighter plane which left the allied soldiers awestruck. Again, the only reason we maintained air superiority was through numbers - we didn't allow any one-on-one encounters because we flooded the sky with planes. There's a certain quality in quantity.
As far as supply lines are concerned, I have to disagree. It was not the length of the supply lines that screwed them up; it was their logistical system. Think about it in terms of pure geography: The Americans had to move supplies all the way across the Atlantic, which was patrolled by German submarines and other ships. The Germans were often successful in destroying a supply ship along with its cargo. However, once again, we sent so many supplies the Germans couldn't possibly destroy enough to halt our logistical system.
The problems with the Germans' logistical system were internal. I outlined in my first post the problem with semi-interchangeable repair parts. Once something broke, it remained broken for a long time. A tank that won's shoot or move is worthless. Whereas, the Americans were able to repair things very quickly and return them to the battle. In addition, Hitler did not see the need to commit his money to things like supply trucks when he could buy tanks. This is a common mistake with dictators like Hitler (actually, Hussein did the same thing. That was one of the reasons we defeated him so easily this time: He had a lot of tanks, but virtually none of them were completely operational due to a poor logistical system. His troops were starving and lacking medical supplies, fuel, etc. before we even started bombing them). Hitler also had a problem getting fuel, medical supplies, food, potable water, etc. up to his front line troops. The system was broke, but it was not due to the length of the supply line. Of course, one could easily argue that the Germans were fighting on two fronts. Certainly that strained the already-broke logistical system. However, the Americans were fighting on two fronts, too, and both of them involved transporting supplies over huge expanses of oceans.
Snowshoe mentioned that other soldiers fought in the war, too. Of course they did - that's why it's called WORLD War II. In my defense, however, I would like to point out that the allied nations were under the command of American forces - they were essentially American forces, because Ike had the authority to use them as he saw fit, just like with his own forces. That is why he was given a fifth star ("General of the Armies"). He was their commander. Even today the senior ranking person in the military - The Chairman of the Joint Chiefs of Staff - is only a 4 star general, and the people who work for him are 4 star generals. He does not get a fifth star because he does not command troops from other nations.
