That's a pretty meaningless statement on the part of Rumsfeld -- he can't hide behind the decisions of generals who he himself put in charge of this operation. Back in late 2002 and early 2003 there was a serious disagreement among military brass about the preparations for the war effort and the personnel levels that would be needed to maintain order in Iraq. The generals who supported the civilian leadership on this won out, so it's rather disingenuous for Rumsfeld to use "the generals" in his defense of the military effort in Iraq.
What military wouldn't want a half a million troops before they started?
Should we have waited?
Check out Tommy Franks autobiography. Rumsfeld didn't write the war plan. Franks and his staff did. Rumsfeld (and Bush) agreed to it. The same thing appears to be happening now with the occupation/transition.
Rumsfeld is claiming he is not dictating tactics (unlike, say, McNamara). I believe him.
He is also saying he is leaving the decision as to what the troop level should be up -- which appears to be the big part of the controversy -- up to the generals in Iraq. Again, I believe him.