Excluding my friends in computer/technology only a small number of people I know feel comfortable reinstalling Windows and hunting down all the drivers (I know how to do it and I personally find it to be an annoying waste of time). None of my nontechnical friends and acquaintances would buy a custom-built PC. I considered doing that when I purchased the systems and decided not to invest time in learning how to do it right (I agree with you that silentPCreview is a great resource for going down that path).
I considered the Mac Mini - which was quiet enough. But to run Windows Media Center I'd have to buy a copy of Windows and to run movies an external DVD which brings the cost up to about $1000. I considered boutique builders like Pugot but they all charge $1000 or more for their better Mac Mini like systems.
I actually started to write a much more detailed article half a year ago that you would no doubt have preferred but abandoned it because I thought only a sliver of systems building enthusiasts would care. My blog usually tries to make technical topics understandable by the masses.
I sometimes share my posts here but didn't consider sharing this post for a second - not the right audience.