Microsoft is moving away from the single-platform; they want their apps to run on Windows, web, Mac OS, iOS, Android, and maybe even Linux. They do not want to maintain radically different versions for all these different platforms.
I know at least one CEO who will absolutely explode if they fuck up his Outlook. He probably have 20 years of business correspondences in there. Is that a good idea? Probably not, but he does. If Microsoft mess up Outlook, then there's very little reason for his company to not look at Google and Gmail, and he probably will just because he'll feel like Microsoft screwed him over.