This is the best one ever I have came across. This helps a .NET Framework developer to understand what WinRT really means. This is all about making the runtime sleek and small. The era started with .NET Client Profile. So when you develop an application which targets specific type of application then why you need other DLLs?
So watch this great talk from Krzysztof Cwalina https://channel9.msdn.com/Events/BUILD/BUILD2011/TOOL-930C