Given Puzo's role with the screenplay, I'm probably too inclined to take the movie as the final, "polished" version of the novel, rather than worry too much about the differences between them.

I guess it's because this is one of those rare situations where a great book emerges as an even greater movie, whereas most Hollywood efforts tend to have very much the opposite effect--turning a great story into a mediocre (at best) film.

But I digress . . . Back on topic: all considered, I think I'm of the opinion that neglecting to have members of the Commission (specifically, Stracci and Cuneo in this case, as fairly major 'background' characters) not give Sonny at least token support at the beginning was a mistake, but granted, not an especially major one. That would at least have rang true with the basic ethos of the mafia--you don't whack a boss without approval--and they could still always have switched sides later, when Sonny's revenge went a step too far (in sanctioning the death of a New York Police Captain).

Still, no biggie.