Oh dear; gnu is at it again.
This is the perfect example of how not to be an open source advocate; promoting a free audio format by suggesting to users that they .... download an entirely new media player.
iTunes users won't give up iTunes just for a codec. WMP users won't give up WMP just for a codec. And in fact there are ways to get Ogg into those players (xiph, the keeps of Ogg have official iTunes support and link from their Windows page to a WMP plugin); but what do GNU do? Push their agenda further, ignoring users, instead of helping users do what they would want.