Courts-Martial for Retired Officers
Yes, as Fred Kaplan so thoroughly explains, retired officers still receiving pay remain subject to the Uniform Code of Military Justice and are still subject to the punitive authority of the Secretary of Defense and President. I suppose the rationale for keeping this legal authority in effect after retirement is to prevent high-profile or large groups of retired officers from undermining the authority of the Commander-in-Chief and other high-ranking civilian leaders. It's a civilian control of the military and checks and balances issue, the argument goes. And, that seems to be a completely reasonable goal, to me.
But as retired officers, they aren't subject to the orders of SecDef or the President unless and until they're recalled to active duty, so they're not being disobedient now. In addition, there's no evidence any one of these fine officers ever failed significantly to execute their duties, even when they claim they were in disagreement with the policy. So how, exactly, is civilian control and good order and discipline impacted? Not much, I'd say.
However, if you're one of those who is truly committed to punishing retired officers for calling on Rumsfeld to step aside, then you've got my "go ahead." And I'll even tell you who the first defendent should be: Rep. John Murtha for calling on Sec. Rumsfeld to step down. He is, though retired, still an officer and collecting pay, is he not?