Prior to Windows Phone 8, Windows Phone 7 was based on CE or compact edition. Developers had to work with only Silverlight, XAML, XNA game engine, C#, or web scripts. Native development was not as strong as it was with other competing platforms because it was not as easy to port apps over by reusing C/C++ code.
This changed when Microsoft engineers decided to base Phone 8 OS kernel on the Windows 8 kernel. More powerful apps were now possible. Cross platform compatibility was also now possible. Developers still use the other technologies, but now game developers can more easily reuse native code to power impressive game experiences. Also, the added horsepower takes away some of the limitations placed on developers.
If you have a Windows phone, have fun playing Halo!