There seems to be a formula for the attraction sequences between Nelson's character and Jeannette's character in this movie and in the others they did together i.e. boy meets girl, girl resists, boy woos, girl gives in, happily ever after. In the end, they belong together.
Given the code restrictions and the norms of the time, just listen to the lyrics of so many of the songs ex. "you were meant for me"," if ever you should leave me", "my love will be forever", the characters were really the songs. The songs told you how the person was feeling.
My mother remembers how mesmerizing her generation felt their voices were together. That really, more than the story. was what drew people in she thinks.