Ah hah! I think I found a definitive post on the topic. Here's a thread on AVS forum. In short, some HDTV signals may soon be broadcast with an evil "down-rezzing" flag turned on. If you've got the DVI connector (and an appropriate tuner box), then you'll see things properly. Otherwise, you may get less than stellar performance from your component outputs.

Now, whether this triggers lawsuits and heaven only knows what else is a fantastic discussion topic.