I'd argue it wasn't as clear that "Windows 10 exclusive" meant "Windows 10 Store exclusive" as Lauran makes it out to be. In years past, plenty of games dropped older OS's while still being distributed through multiple storefronts. There was every reason to think Microsoft would be widely distributing their games—not least the appearance of Steam during Windows 10's announcement. Or that Phil Spencer once told us, "We're not trying to say that the only way you'll get games is through the Windows store." Or that Kevin Unangst once told us, "We are not intending to compete with Steam. If anything, we want Steam to be even more successful."
While not confirmed, it suggests that any Microsoft game announced as "coming to Windows 10" will be distributed solely through the Windows 10 Store. That, potentially, could include Rare's Sea of Thieves and the recently announced Halo Wars 2. We'll try to chase down some clarification about what's releasing where.
