I've always agreed with what Wayne said about Rocco.

No where is it implied that it must be Rocco himself who carries out the hit on Roth.

Yes, Rocco was made responsible for Roth's murder, but had he come up with a different plan that did not involve himself as the shooter there's no reason why Michael would not have approved it.

AAMOF, if Michael viewed it as a probable suicide mission, why would he rather lose Rocco instead of some unnamed button man who was lower in the pecking order?

Despite the fact that, as Turnbull correctly and never boringly points out, Neri had pushed past Rocco in importance, Rocco was still one of the three key people in the upper level of the Corleone organization.

Interesting, BTW (I think, anyway), how we always refer to Rocco by his first name, and never by his last (Lampone) and Neri by his last name, never his first (Al).