cattletruck,
Microsoft do develop products for both Apple OS X and Apple iOS, as a result they maintain extensive well-equipped Apple lab facilities.
As well as direct product development, to give them their due, Microsoft have been making inroads into resolving historical interoperability issues between Windows Server and Apple (and Linux).
Going beyond that, staff and visitors to the Microsoft campus will no doubt be allowed to use whatever they want to use, like many corporates these days, Microsoft no doubt run a BYOD policy.
Or maybe, after god knows how many attempts at trying to make a Windows Phone that actually works, they've given up trying to force their staff to use them ....
