Agreed, Oli. But as always Vito had a way of putting things that Michael lacked. Michael says "You're out" "You're not a wartme consigliere."

Vito says "I never thought you were a bad consigliere, I thought Santino was a bad Don, rest in peace, but there are things that you must not be a part of...." He is sending Tom a clear messaage about his abiding affection for him and his understanding that Tom is and always will be loyal.
There is a direct correlation between Vito saying these things to Tom and Tom's very tough stance in Vegas when Fredo tried to appeal to his sense of reason and bargaining. Tom says that Vito is semi retired, and if you have anything to say, say it to Mike. Translation: If there was some division in the family over Tom's abilities, or Mike's plans, Tom makes it perfectly clear that while Moe is right about the Don being sick, that Mike is running the family business, and there is no going over his head to appeal to Vito.

That's why Mike...ever sensitive to any hint that he is not totally in charge...levels the threat to Fredo "Don't ever takes sides against the family again....EVER."
Vito would have said "I think you're going soft in the head from all those cocktail waitresses you're playing comedy with. Don't ever tell anyone outside the family what you are thinking."