I firmly believe that tools like Reflector and it’s decompiler actually make the .NET platform a more attractive environment to work with. Developer documentation is always insufficient (if not downright inaccurate) - having instant, easy access to the source for any (managed) component - especially the BCL itself, makes a developer far more productive, and thus makes the platform itself more appealing.
I personally find Reflector every bit as useful as downloadable source - maybe more so, because it doesn’t involve downloading big code bases, mucking around in Visual Studio, etc. I’ve never felt the need to download Rotor, for example.