It's 'my oppinion' that Michael suspected Rocco's involvement and therefore tested his loyalty by sending him on that ridiculous mission.
So if Rocco were guilty, but he were successful in killing Roth and surviving himself, you think Michael would have let him live because he passed the "loyalty" test?
"I got news for you. If it wasn't for the toilet, there would be no books." --- George Costanza.
