Of course, The Godfather Trilogy I assume refers to the movie, so we're in the movie's universe here. And, the Godfather book universe and Godfather movie universe are not necessarily the same. Take Fredo for instance, who isn't nearly as "stunad" in the book as he is in the film. They made him weaker in the movie to to play off of Michael's strengths. Old showbiz trick.

That being said, I agree with Olivant that the book can fill in gaps that the movie doesn't completely address.

"...the successful annihilation of organized crime's subculture in America would rock the 'legitimate' world's foundation, which would ultimately force fundamental social changes and redistributions of wealth and power in this country. Meyer Lansky's dream was to bond the two worlds together so that one could not survive without the other." - Dan E. Moldea