Ok, maybe so, but there's another explanation that could at least be considered; namely, he had to go because his ability to run DOD is over. Beginning in January, he would have been spending 5 days a week on Capitol Hill being raked over the coals by various Senate and House committees.
And since he had to go, it had to be ASAP,
1) So Bush's new guy could be voted on by the still-Republican Senate.
2) So it wouldn't be after a week or a month of Democrat congressmen publicly gloating over what they would do when they got Rumsfeld in front of them. How ignoble would that look?
3) We don't even know he didn't resign. He may have just informed GW that he didn't care to spend the next year as a Pinata for the democrats. In which case, See 1) and 2).
Just a thought.
Ping to some sense.
wise thot