The most significant part about the Mac mini which makes it a shitty HTPC is that it's got a fan. And can't/won't do much more than a $200 dedicated box will in that role. Yes, you can run SageTV on it with some external capture devices. You can even run EyeTV (a Mac-oriented PVR) if you wanted to. But it's still got that fan.

I'm sure Apple intends to update their AppleTV. But I'm also sure it's not going to play all the codecs and container formats and will still be tied to iTunes in at least some way.