Just curious: is that "known as a fact" now? I'd imagine that means that their own data center for iCloud is running Windows Server, too. Which doesn't really seem any less likely in today's world than Linux servers but it would be interesting just in terms of how much you could blow Apple fans' minds if you could travel back 15 years and tell them that.
EDIT: I'm wrong, as pointed out below; Azure isn't just for Windows Server.
EDIT: I'm wrong, as pointed out below; Azure isn't just for Windows Server.