Office too, has a strong dependency on AD. AD is how Office documents are protected (rights management), how they're synced to Office 365 (WS-Federation -> AD),

Office too, has a strong dependency on AD. AD is how Office documents are protected (rights management), how they're synced to Office 365 (WS-Federation -> AD), and how they allow multi-person, simultaneous/real-time editing. Amongst other stuff.