For most of your points i would say RTFM, but i'm in a good mood
Point 1 : If i'm not mistaken, it will be included in the future versions of Windows. It's already in Win2k3 server.
Point 2 : .NET also runs on Win2k/98/Me/NT.
Point 3 : If you leave them in IL, you can use an obfuscator and still get all the benefits from the IL. You can also compile them to native code (like a Win32 app) but you don't get the IL benefits.
Point 4: see gmily's post
Point 5: Tell those user that .NET is what makes sure that Windows app work secuerly and smooth. And that it's the future for windows apps, and possibly also some *nix apps (mono).