Pretty interesting slide in Krzysztof Cwalina's talk: http://channel9.msdn.com/Events/BUILD/BUILD2011/TOOL-930C about the surface area for .NET metro apps. Note that the count on the .NET Metro APIs do not include the WinRT apis.
  .NET Metro .NET 4.5 Windows Phone
# assemblies 15+ 120 22
# namespaces 60 400 88
# types ~1k ~14k ~2k