I still find this a very strange decision, for two simple reasons.
1. Rocco is a caporegime. He's therefore an important member for the organization and it's structure. Other's in the organization may also be angered by that decision and might question Michael as their boss.
2. As he is a caporegime he is closely connected to Michael, who would very quickly be suspected by authorities which turns on heat.
Brings me back to what's been going through my head since I saw II. Sonny would have used Rocco to pick a soldier to carry out the hit. It's the chain of command, what insulates a boss from the authorities. Michael follows the chain of command with the New York faction, communicates though Pentangeli. But not with the murder of Hyman Roth. Given the circumstances, the hit will be the most highly publicized murder of his time. Bizarre, what a mess.
Best explanation I can think of, when the Feds land a shot on Rocco, it would have an emotional impact, whereas the death of a random soldier would not. Perhaps it reflects on Michael's self-isolation, yet another example of how he is harming those close to him. This is juxtaposed with Frank's suicide, which Michael orchestrated. Tom was moving away from him, Rocco and Frank are literally dead because of Michael, and by the finale, Michael has killed his OWN BROTHER. Best I can think of. Anyone else want a crack at it?
