Just a couple minor things:
Windows PVR software:
Nvidia includes Intervideo's solution.
ATI AIW come with their own PVR program. (Which is excellent.) ATI AIW's are also natural video capture cards. In their price range they have no equal.
There is also Beyond TV.
You neglect to mention a PC's audio jukebox capabilities.
The new Envy based sound cards are much better than the Turtle Beach one for audiophile level audio. (Creative takes the cake when it comes to gaming though.)
ATI has the HDTV Wonder which allows both for ATSC tuning and HDTV PVR.
Also might want to go over the current state of component output support and DVI output support.
IE: ATI has better component output support, but it does not currently have HDTV specific DVI output support.
Just thought I'd expand upon this since there was some questions about it. ATI cards can and do put out HDTV resolution via DVI which will work fine for projectors and for TV/Monitor hybrids. According to this article however it seems that an ATI card will not put out to a strictly HDTV TV via DVI. If you read the user posts after the article this is apparently because the ATI card will not open its DVI port if a proper EDID is not present. However, a user was able to force it using PowerStrip. (An extremely useful program that I use myself.) Hope that clears it up.
There are also "Windows Skins" for lack of a better word that can take control of the PC for all media stuff. IE-myHTPC (haven't used it before though)
You may also want to mention, in brief, about the availability of fans, power supplies, etc. that are extremely quiet.