HereForTheBeer: On the other hand, maybe - and it's likely the slimmest of maybes - maybe that will open the door to Microsoft bringing some old games here once they take a look at the contract, sales numbers, yada yada, for the title(s) they just bought.
I think MS has a history to use also games to "entice" (or force?) people to move to new OS versions or services, like how Halo 2 PC required Wiindows Vista IIRC, and I recall they did a similar move with some other game with Windows 10. Also they did keep Age of Empires remake as Windows Store exclusive.
That is their prerogative of course, too bad for those who'd like to buy it outside of Windows Store. MS probably cares less of the potential sales of some games (by releasing it outside of Windows Store), compared to using it as means to get people to adopt their new service. Heck, even GOG is offering some freebies to get people to their service. :)