My PBS has two 1080i, a 480i and a four channel audio channel with slides. The stills look fabulous, but the high delta stuff is absolutely nauseating.My new KLCS/KCET CSA has two HD channels (720p), and 4 SD ones.
I've found this to be true as well but some of it comes down to bloodying the SD content to preserve some resemblance to HD on the HD channels. I think a lot of it comes down to passing the signal through image processing software to make the content more amenable to compression and multiplexing.I think TV stations' multiplexers are better at doing multicasting now ....