What Comcast did here, is after the federally mandated end of analog transmission, the corporation basically took advantage of consumer confusion, and axed everything under the 100 channel range (which I was perfectly happy with receiving) except retained 2-13 plus a few crappy other ones that no one watches.
We have one digital TiVo HDTV and one analog TiVo CRT TV. The analog one gets 2-13, the digital one gets the whole 1,000 range. The digital TV requires a CableCARD (actually two of them, because we're using older technology) and while they provide the first for free, the second is rented.
A box is required for that TV as it is basically just an LCD monitor -- the only choices are one from Comcast (which is a Motorola or whatever) or something from TiVo. Or at least last time I checked.
MythTV seems interesting, and I would probably throw one together for the heck of it, but since it won't work in my area, due to the CableCARD requirement, not gonna happen. If there were some sort of solution of using MythTV with my cable provider, where I'm not stuck in the 2-13 zone, it would be a different story -- however, until someone educates me otherwise, MythTV is never going to get anything to accept CableCARDs -- because in order to decrypt the signal, it would basically open up a massive world of piracy.
The media corporations have been against the entire concept of the original VCR, since inception, and they finally got their way.