This has been a long time coming. Microsoft Play
just added has (see update below) 15 Xbox Live Arcade games to Windows 8 and RT through the Windows Store. And it's about time.
When the Windows Store launched, its ability to unify games across computers made it seem like a natural fit for XBLA titles. But the fragmentation between Microsoft's various stores quickly because apparent through missteps like the Mature rating flub. This is an encouraging step toward getting all of Microsoft's stores (Windows, Xbox, Windows Phone) on the same page.