Took the words right out of my mouth.

You forget. This is the military we are talking about here. They want it to work. Redundancy is good. But it must be able to be destroyed in case of emergency. Batteries wouldn't be considered redundant enough because they may be drained.

Actually, you make a good point but volatile memory is considered just that: Volatile. Therefore it cannot be a trusted storage method. It may also be harder to protect against EMP..