In the film Michael has the heads of the other four New York families assassinated.
These include Barzini, Tattaglia, Cuneo and Stracci.
In the novel, it is only Emilio Barzini and Philip Tattaglia that are assassinated.
Is there any explanation in the film as to why Cuneo and Stracci are also murdered? If I remember correctly it was only Barzini and Tattaglia that conspired to murder Vito and later Michael Corleone. I can't remember a mention of Cuneo and Stracci getting involved?