George Lucas might have been lead creative mind, but McCallum was the man in charge, pulling the strings. He was one of the very few who could have stood up to Lucas when he has made a bad decision.
He deserves at least as much of the blame for the lack of quality in the special edition and prequel trilogy.
Edit: I wrote this comment before reading his quote from Total Film or any of the other comments in this thread. Right now, I have no respect for the guy (I refuse to call him a "man", because that is not what he is) whatsoever any more.