Other mistake: The close up of the Wall Street Journal mentioning Immobiliare seems to have operating instructions for a Windows program under the headline. The newspapers previous to this appearance also have a headline pasted onto another news topic altogether. The same happens later with the newspapers covering cleansing actions of the new pope. These papers date from March 27, 1980, although the events are supposed to take place in 1979. (00:41:42 - 02:00:00)
Other mistake: Before Joey Zasa is murdered, an altar boy in the parade (on the left side of the screen) can't help but stare at the camera all the time.
Other mistake: In the Mafia World, Vincent would have never been appointed boss of a family without first being initiated as a full member of Cosa Nostra, working his way up the ladder from soldier to Capo, etc. As far as we know, Vincent, from the beginning, was only an associate working for Joey Zasa, then starts tagging alongside Michael, who gives him control of the Corleone Family later, after his failing health.
Other mistake: In the mafia world of Cosa Nostra, anyone that puts their hands on a made member, especially a low-level associate such as Vincent, would be immediately killed. Vincent would not have been allowed to live for viciously assaulting a mafia Capo, as was the rank of Joey Zasa in the film. Not even Michael could have saved him from such a fate had this been true.
Answer: It shows you how greedy they are even as they've made it to the zenith of their criminal careers. That's why you see Michael pass it on disgustedly and stare blankly into the ether. Michael's goal was never to be the boss or capo di tutti capi, he only did it to protect his father and then his family, his main goal. And at that moment he realises he's never getting out. He's a business man in a world of criminals (which he is himself).