In browsing around the Silverlight installation directory I see a number of framework DLLs as expected. But I also see a separate DLL with the same name but with .ni inserted between the dll name and extension. For example there is a System.dll and System.ni.dll. There appears to be a sister .ni dll for almost all of the system dlls. Looking at the quickly in Reflector they appear to include the same content, but are much bigger in binary size.

Just out of curiosity, can anyone explain what these are?