Hi there, I work for the client platform team here at Microsoft and thought I'd take this opportunity to quickly answer the valid questions you raise.
Firstly, we're not trying to hide anything in terms of developer APIs or documentation. We've got a good set of reference material online that is targeted at someone developing Silverlight content for display on a website. On the other hand, Moonlight is developing a compatible implementation of the Silverlight runtime, which is a pretty specialist requirement. There are different needs that Miguel and team have - for example, how to parse ill-formed content, and there are internal development specs that will help in making a 100% compatible implementation.
Secondly, the codecs themselves are licensed implementations of the VC-1 standard. We're not in a position to put them into the public domain, unfortunately, but making binaries available at least exposes the functionality.
Hope this explains where we're coming from and dispels at least in part the perception that every strategic move has evil intent!