Even for power users, HTPC's can be aggravating. Why, in a world where you could put together a tiny monster PC for around $300 would someone buy a MivX or NMT player? Simple. Take any HTPC on the market, ANY.
Plug it into a regular, yellow, composite television.
Plug it into an HDTV via component or HDMI.
If you can turn it on, boot it up, and play a video on it without a single configuration edit without any hassle from installation, then please, reply to this topic because as far as I know, an HTPC that does this is akin to a fucking unicorn.
I have an iStar Mini and a Popcorn Hour, both NMT devices. The Mini's in the living room. If I wanna take that thing to the kitchen TV (13", composite in), I just put the movie on a USB stick and it's showing the film inside of the 2 minutes it takes to set up and boot. When it goes back to the living room, it's an HDMI connection to the TV and coax to the (admittedly cheap) surround system. Works just fine, automatically detects 1080p at startup. Over component, I'd have to hit two buttons to get 720p or 1080i (worst-case, 480p is instantly automatically enabled).
I had a friend try to build a MythTV box. Hours went by as this man tried to get MythTV to show up at a decent resolution on his HDTV (this was a few years ago, via DVI). This is a guy who runs and actually knows how to use Gentoo, and would be a sysadmin if he wasn't a programmer at a Fortune 500 company (A good one, you've probably used their services at some point(s) in the last six months). On the AppleTV, the first test isn't even a possibility without some insane level of hacking (especially if you want color out of the composite out). I can only IMAGINE what it's like an a Windows Media Center rig. And in the last two cases, playing videos other than Quicktime or WMV, respectively, (let alone something like MKV) is a hassle that goes more hours into getting up and running than those devices are probably WORTH.
As crappy and low-end as the interfaces are on mini video boxes are, they happen to work remarkably well for the simple process of "Plug into TV, watch stuff", whether "stuff" is on a usb stick or the network. Give me a call when the HTPC manages to get there on a remote-friendly interface.