If we were to organise ourselves properly, the forces do represent a large economic bloc that could arrange some fantastic deals - certainly way better than the nonsense in the Forces Discount Brochure and more akin to the US forces.
The problem is we won't ever get sufficiently organised and, as is the case with many good offers, Cpl (or Capt) Miggins will try and cash-in on it either for the benefit of his non-entitled 43 extended family, or as a means of making money by re-selling whatever the discounted item is. Human nature, I'm afraid - just look at the number of people caught shipping back 80,000+ tabs a few years ago. Generally, the Americans follow the rules.