According to an official Activision support page, both games will be available for separate purchase through Microsoft’s storefront. These will be entirely separate products from the Xbox One versions of the game and won’t take advantage of the Xbox Play Anywhere initiative. This eliminates both cross-platform multiplayer and purchases between Windows 10 and Xbox One, requiring two separate purchases to play on both platforms.

While it’s somewhat expected that Xbox One players and PC players should be separated, due to the accuracy gulf between controllers and mouse players, it’s a little unexpected that Windows 10 Store players will be isolated from other PC versions of the game.

Source: [Updated] Call of Duty Infinite Warfare is coming to the Windows 10 Store – with caveats

So… why buy from Win10? Dunno…