Orac,
You might want to confirm that statement....when I was in the Army it was up or out for all ranks....two passovers and you were gone.
The bad part of that system is one has to please his rater or suffer a less than stellar evaluation and you are dead in the water for all future promotions. That is a system that breeds "Yes Men" and not war fighters who think on their feet and take initiative.
There is a thread here now about just that sort of thing in the British military regarding secondary duties.