Attenborough once spoke at my college and someone asked him about the changes. He was very non-committal saying they were just choices they made that they thought would work better on screen.
Bishop is wrong. Her character is the older one but some of the characters are younger. Mark explicitly says he's never been in a Broadway show.
I'd guess Let Me Dance for You was put in for it to be more of a love song about Zach and not about dance (just like the movement of What I did For Love from Diana to Cassie.
