Keep in mind that authors and script writers have to inform the audience about characters motivations, etc. and about the relationships among characters. If you didn't read the novel, then you wouldn't know about Luca or his relationship with Vito or how Vito was involved with Johnny. If Michael doesn't introduce Tom by his last name, then you Kay doesn't ask about that and Michael doesn't get to tell the Sonny found Tom story. It's all foundational.
I understand what you are saying and its a valid point. I just think there is a major difference in telling Kay about Tom and how his father conducts business with an associate as Luca.
