Game Developers using Visual Studio are able to create games that can be made cross compatible between Windows (Microsoft) Operating Systems, including Windows Phone 7 and the Xbox 360. 90% of the generated code is the same between the various target platforms, leaving about 10% for platform specific stuff. Perhaps one could look at it as some sort of SDL-layer?

In this article, Microsoft demos a cross-platform game that can be run on a computer with Windows 7, a mobile phone 7, and the Xbox 360 console. A video shows how a Microsoft employee starts the game on one device, continues it and finishes it on others. The progress made within the game is automatically transferred from one platform to the other - probably by use of the Windows Live platform.

Windows Phone 7 development is mostly done with Silverlight and XNA.

Cross platform gaming between PC and Xbox 360 was possible before, just take a look at the game Shadowrun.