I think some of the issues might be "Copyright" - for example playing commercial DVD's requires the use of a decryption algorithm. In SOME (but not all) jurisdictions a royalty fee is payable for the use of this algorithm. VLC has AFAIK reverse engineered it -- totally legal in some countries) and therefore can be downloaded FREE.
Things like FLAC for example are open source but there are other proprietary codecs that require the use of either "licenced" libraries or Non open source facilities which might require a royalty fee.
If WMV hasn't "coughed up" then it's no go for playing those codecs -- Ms can't put itself in the same category as VLC and other "Quasi Legal" players.
(Now whether or not this whole area SHOULD be open source - and the whole ridiculous regionalisation thing for DVD's be abandoned is another issue !!).