Ten years ago, a common assumption was that 45 million bits per second were needed to obtain studio-quality television. Today, that level of performance is possible at 4 million bps. There is one fundamental reason for this profligate use of bandwidth. TV receivers are dumb - in particular, they are forgetful. Even if you compress them by taking out the enormous redundancy that occurs within and between frames and by taking advantage of the characteristics of human vision, video as we know it still uses many more bits than a computer graphics database capable of synthesizing the same images.
Inefficiency also results from a lack of memory.
Your TV doesn't remember that the set of the local news changes only about once every three years, it doesn't remember the architecture of sports arenas, and it doesn't remember the Steve Forbes commercials seen six times each hour by those of us living in states holding early primaries. MPEG-2 may be among the last standards for which anyone bothers to develop a dedicated chip. Because a single data standard for digital video, one that is always best, just does not exist. Your TV's decoding capabilities might be updated as often as your PC's Web browser is now. Perhaps TV viewers in the next decade will eagerly look forward to September as the month when the next season's algorithms get downloaded.