MS attempts at media extenders goes back quite some time, it's not a new thing, just a new name for an old idea they had that didn't sell very well.
But it's true that with the new home server that keeps track of backups, media and other stuff along with WinMCE they are beginning to get there, what is funny with MS extenders though is that you can't play content that is not on the WinMCE machine.
Unless they change something you can't access files on the MS home server from a 360/extender connected to a WinMCE machine, it's not possible (or atleast didn't use to be), you can see and play the media fine on the MCE machine, but not on the extenders... you can't even forward TV content from the MCE to an extender (I have heard, but this I am not certain about) That is on of the things that made me look elsewhere.