Having hardware h264 decode may seam like a big deal, but when you had the money to get a 6800 series GPU, you were not worried about your computer being capable of decoding h264.
Having that tech on 6600 series GPU made a lot more sense as that card is usually paired with much weaker computers. Even so, the vast majority computers at the time had no problems decoding h264, hence:
"This tech is nothing to write home about, just something engineers have been toying with. If useful, it will be included in (x+1)80x cards later on. "