Well, now you raise another point, dt:

I think greed for Roth's Havana gambling empire blinded him to a fundamental question: Why would Hyman Roth be taking the Rosatos' side in an internal dispute with Pentangeli in New York City? Why would Roth--based in Miami and Havana--care? We know from the denouement that Roth was backing the Rosatos in his bid to simultaneously kill Michael and neutralize NY by having the Rosatos get rid of Michael's man Pentangeli. But, Michael didn't know that prior to the Tahoe shooting.

He should have questioned Roth's interest in this seemingly internal dispute. Perhaps he did. If so, I can envision Roth telling him, "Michael, just go along with me on this--it'll be good for our Havana deal." And Michael probably bought it.