Flag staff in DoD use blackberry because their IT goons are scared shitless of telling their dyed-in-the-wool-msft-fan bosses that a UNIX-like operating system is good business.
It's that Blackberry with BES has actually decent management and security, unlike a cobbled-on-Android MDM, and the Blackberry keyboard.
The underlying OS on the Exchange server doesn't matter. That DoD is (I'm pretty sure) the world's biggest MS deployment does matter, though -- even though I prefer UNIX, if I'm in an environment where 99% of systems are Windows based, I'd build my ancillary systems on Windows, too.
