INHO, the WO program isnt' really 'cheap' labor if you consider the big fiscal picture. The retirement pay isn't really where the gov't spends its money. The healthcare is and there is no difference in the cost of a E-7s health care vs an O-6 to my knowledge. It's the same reason the military outsources contract maintenance in the production sources(TRACOM/FRS). It's way cheaper to pay a company a set fee than it is to plan for those retirements or a percentage of them down the road.