CNet has a story titled "High-def TV not ready for Net's prime time" that is worth the read. Of course it is a very controversial subject as some sites claim they stream HD quality video and several companies are working different technology methods to stream HD for Internet TV.

However, the article goes onto say that HD over the net is a ways off because the pipes just can't handle it yet. "In fact, every industry expert interviewed for this story said that the way things stand now there just isn't enough bandwidth going into the home to stream the more expansive HD video."