I didn't say it was 'unimportant'...but that it had no place in the film. And it didn't.
I think a better word would be 'unnecessary'

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The goal in the making of the film was to get Michael home and get on with the story. The meeting of the Dons called by Vito after Sonny's death pretty much fulfills that obligation, without the need to include the vast (yet interesting) details of the Bocchicchios.
In the film, we don't need to know HOW Michael gets home...just that he gets home and proceeds to take on the reigns of running the Family Business.
As I've said before...I enjoyed the movie for 20 years before ever setting eyes on the book. While I thorougly appreciated this particular aspect of the story, I can tell you that its lack of inclusion did NOT leave the movie lacking in any way whatsoever.
But...perhaps they can make a big deal of it in GFIV

!!
Apple