The US ARMY and Apple have been in talks for years and it is clear that Apple isn't desperate enough for the ARMY's biz. That is, Apple doesn't want to bend enough to satisfy DoD security requirements for both mobile and desktop devices. The ARMY has had a big fat check with Apple's name on it for years.
Most of the DIACAP, etc. requirements are either reasonable or purely policy enforcement. It seems like it should be possible to implement most of the policy restrictions using Apple OSX Server or another management platform, rather than lots of UI/UX changes on the clients.
Makes sense to me. They want to secure it and they need to stick with a tried-and-true platform. What's the point of upgrading if there's nothing wrong with 2.2? Only consumers need the new feautures, in my opinion.
There are some significant performance improvements with later versions that would be worth having (better GC, for example).