While it was a decent subplot in the novel, and served as another example of how Don Vito had risen to power, I really don't think that it would have made that much of a difference if added in the movie in establishing Vito's power.
If anything should have been added from the novel, to the movie, it should have been the background story of Luca Brasi. A very interesting story in itself within the novel.
Don Cardi
Five - ten years from now, they're gonna wish there was American Cosa Nostra. Five - ten years from now, they're gonna miss John Gotti.
