Isn't Superman theatrical in the box set?
Weird things happen between remasters sometimes. Mary Poppins has more info at the sides in 1:85 than it does at 1:66.
One thing I've noticed about the Criterion Grail is slightly more info at the right of frame. The Blu has more picture at the left of frame.
When I get the discs in, I want to do some screencaps. Is there any particular shot you'd want to see?