New compression algorythms.
Sorry, but no.
The Discovery quadruplets appear to broadcast 4:3 SD content at a crop that leaves small black bars on either side. Maybe 15:9. Looks to me to be a straight crop and not stretched. The crop also appears to be dynamic; I've seen it jump around to different ratios during commercial breaks. It looks like it could be doing a straight 16:9 crop on 4:3 commercials filmed with black bars on the top and bottom (phony HD). I saw some commercials at full 16:9 that sure didn't look HD.
One thing I don't understand is why older shows like Mythbusters -- which has been shown on Discovery SD with black bars on the top and bottom for years -- are being broadcast with the small black sidebars instead of in full 16:9 (especially if they are using some sort of dynamic crop).
I guess we'll cut them some slack in their first few days.

Especially since what they do show in HD is almost all stuff we haven't seen in HD before, on HD Theater or elsewhere. If I'm not mistaken, it's the biggest single simultaneous rollout of related networks into HD that we've seen so far (other than the Voom networks, which don't have to deal upconverting SD into as they don't broadcast any.) And I guess HBO's upcoming HD launch will be bigger as well.