I'm thinking that the reason that they are spending the 60 billion per year to keep the current technology viable is because it would cost in the mid-trillions to replace/change the computers. Changing any technology platform takes years in order to scope it out properly. They also have to be careful from a security perspective on how they engage any upgrades. I'm sure that the global expectations that the US be the sheriff of the world (and paying for it) also takes its toll on the amount of R&D procurements that they intend to complete in any given year.