content: DoD buys the full software, but is reworked by subcontractors, and M$ themselves to create a distributable version of the software tailor made for each branch of the service, as they all tend to have different needs as driven by different requirements set forth by commanders who are advised by subcontractors as to what the best thing to do with their software is.  the reason theyre transitioning to 10 is likely because M$ "sunset" win  7 and 8, and they are required to transition by regulation.  typically M$ will provide 10 years of support after GA date, but they wanted people on 10, so... yeah.