The point is that the supposed cost of storing spares, retaining older kit is founded on civilian practise, and which may not be appropriate in the military environment. It may be economically sensible to sell off defence estate (including storage bases) but RAB takes no account of the fact that it's strategically insane, and seldom takes account of the fact that defence estate oftenh has to be sold back to the original owner at 1930s or 1940s prices.