Hi Ray I tend to agree with most of what you wrote. I would only differ with " He is not blessed with a perfect singing voice ". I have heard Dave sing a French Sea Chantey in French. He sang it so well I wanted to complement him on his rendition of it. But Dave was at the end of the night all over the Guest Like a Rash trying to Blag a CD to review so I did not get the chance.
I have thought about Dave the possible reasons for the marked difference in his delivery of this song. I came to the conclusion that Dave had actually as you pointed out learned this song and because he was concentrating on its French Pronunciation, it stopped him from, singing with his mouth closed this is what normally restricts his voice. As you were pointing out Ray singing from a Book unless you hold it very high causes singers to restrict their voice and transmit it down into the carpet. The Carpet on other obstructions does tend to kill the tonal qualities of ones voice. Singer not reading from a book is also able to make eye contact with the audience and to add some feeling to their song.
Please think about my last comment, everyone!, as nobody could say that Bob Dylan has or had a great singing voice without the feelings, passion and belief in what he sings.