It's called USDP - Unifying Single Developer Platform. By having a single developer platform they make sure that developers have streamlined approach to application development. This is also illustrated by Visual Studio by allowing you to easily switch between Windows desktop and mobile target platforms.
This isn't new in any shape, either. It has been long strategy by Microsoft and can be seen from DirectX to XNA to C# and .NET. Microsoft wants to create unifying access to developers and this has also been one of the major successes of Windows OS. Why change something that is good and works?
