Noisy? You can barely hear my gaming machine at full load, let alone my HTPC...
HTPCs are nice, someone simply needs to package them preconfigured with a few of the customers predefined specifications and you'd have a winning package. You can build a freaking awesome HTPC these days for really cheap, talking $500 for a great system that will age very well thanks to the functions it does. So price isn't really that bad. It's just no one has a use most of the time. Besides DVR functionality few people have large enough movie collections, music, or want to use the other features at their TV. Give it a bit of time though, DVRs will slowly evolve into full fledged HTPCs.
That's good for people who like to build PCs.
What about people who don't, which comprise the majority of would-be HTPC users?
Where's a pre-built HTPC box for $500 with Vista or MCE, with a remote, which is quiet and has a 1-year warranty (something that Visa/MC/Amex would warranty for another year -- they won't warranty white box PCs)?
And, for a lot of people, that thing has to work out of the box, without installing software. It has to work with cable or DBS systems without separate STBs.
Because you can get DVRs which are also tuners for cable or DBS for way way under $500.
Yes there is more functionality, like I don't know, watching downloaded Xvid videos or whatever but the mainstream audience isn't going to wait hours or days to download torrents.