If you stop to think about it, the survival of the musical as an art form is one of the miracles of the 21st century. Musicals are expensive, complicated and old-fashioned in their unreal mingling of song, dance and theatre. They are also incredibly hard to pull off successfully.
By changing, the musical has remained a truly popular form because it has shown itself capable of speaking to new generations. They grow up on Gene Kelly, but end up loving Velma and Roxie