DVD Talk Forum - Blu-ray vs Comcast HD movies

hey guys...new to the forum and new to HD. I am more than pleased with the picture of the Sony Bravia 46" 120hz machine. The picture and clarity is stunning. I am however less than impressed with the blu-ray movies I've played using the PS3. While nice, they certainly aren't as good as the demos at the stores and are not as clear as the Comcast full screen versions of the same movies.
I recently compared Superman Returns and the Comcast broadcast was better than my PS3 connected using HDMI...not exactly what I was expecting. Here's the odd part. When I watch trailers and the disclaimer messages, the picture is wonderful. As soon as the movie starts it gets less wonderful. I went thru the recommended tweaks from some website to no avail. So far I've watched "The Prestige", "X-Men Origins", "Night at the Museum 2" and "Superman Returns"....What am I doing wrong?