Al, he is reading the manual correctly. According to the manual, you must use an oil that meets the Ford Spec for motor oil to maintain your warranty. The only oil that meets the current Ford spec is 5w20, because of the way the spec is written.
Ford has not used temp ranges and different viscosities for many years now. They recommend one grade, and one grade only for all conditions in nearly all of their gasoline engines - and currently nearly all of them call for 5w20.
On the 4.6l, no changes have been made to the motor between motors that called for 5w30 and those that call for 5w20. Yes, the primary motivation was for corporate fuel economy.
Those things being said, and based on what we have seen on UOA's of 5w20 so far, I'd have no problem using the 0w20, and no problem using 5w20 (the motorcraft oil is showing well). If I couldn't find those, I'd use 5w30.