Again, who cares what the employees personally use and like? That's none of my business. It's just that at work, it should be strictly Microsoft (With the exception of things like laptops, tablets and phones, because Microsoft is trying to encourage other OEMs to get on board). Yes, it has competitors everywhere, which is why it's essential it maintains its image everywhere.
A slip up in one category could speak ill for the entire company. Windows Phone is struggling as it is, and it's just embarrassing (to the platform, anyway) when seemingly, even Microsoft employees aren't using it. Sure, it doesn't mean anything, but it still looks bad.