Originally posted by BryanSD
I'm of the opinion that it has more to do with 720p vs 1080i broadcasts than the KELO/UPN subchannel. 1080 interlace gives us 180 less lines at a single instant in time than 720p. If you take a look at past threads, about the only time anyone complains about KELO's brodcasts is during sports events. Meanwhile, slow moving CSI looks fantastic. We're comparing apples vs. oranges here...
The pixelization/macroblocking you see with 1080i isn't an interlace artifact, which would look like NTSC jitter, but rather it's a bandwidth problem - when lots of pixels change on the screen simultaneously (fast motion scenes), there simply isn't enough bandwidth to get all the information down the pipeline. So you get pixelization around the fast-motion areas, or across the entire picture during a fast pan, for example.
720p displays slightly fewer pixels per second, but its real benefit is that it compresses more efficiently under MPEG2, requiring less bandwidth to broadcast, and therefore its picture quality doesn't suffer nearly as much as 1080i. Given sufficient bandwidth, say 19mbits/sec, 1080i sports can look great (HDNet is 1080i, for example), but that doesn't leave any bandwidth for stations that want to add subchannels. So there's a tradeoff for 1080i vs 720p - 1080i offers more resolution, but 720p is smoother for action scenes. I personally prefer 1080i for movie and documentary programs, but I like 720p for sports.
For multicasting TV stations, 720p is a win. The 720p HD signal doesn't suffer much degradation at reduced bandwidth - I think KSFY sends out their 720p at ~12mbits/sec, for instance, and it looks fine. Compare that to KELO's 1080i at ~15mbits/sec, which has lots of artifacts during sporting events despite a higher bitrate.