It was a nice, subtle touch, true to the novel in its own way. In the novel, Hagen approaches Johnny (well before Mike's trip to Vegas) about signing a personal appearances contract. Johnny says that if the Don wants a favor, he has to ask him personally--Johnny won't do it just on Sonny's say-so. Hagen is impressed with Johnny's common sense for recognizing that hothead Sonny might ask for something rashly that wasn't in Johnny's best interest. "Your godfather would never ask you to do something you wouldn't do for him anyway," sez Hagen.