It's interesting that if Puzo had simply written: "To arrange the peace conference, the Godfather called upon the head of the Bocchicchio Family. The Bocchicchios had a territory in the Hudson Valley, and controlled the garbage hauling business there. They were traditionally called upon to act as intermediaries in time of war" then few would question that they they were the sixth family.

The full quote from Puzo is that the Bocchicchios carried a strain of stupidity, "or perhaps they were just primitive." It brings to mind the passage where the doctor sees Vito as an ill-dressed peasant, while conceding that that peasant carried a bit of folk wisdom with him.

One of the recurring themes of the book is that IQ is not everything, and can sometimes be an impediment. The Bocchicchios "are clever enough to make a good living" and that's really all the brains that they needed in their world.