I think DVDs are 24 bpp, and some of them look pretty bad. If you pause you can see loss of colour (dynamic range anyone?), let alone mpeg2 being an old codec, all sorts of artifacts, if you get a smokey scene you are nackered! (aliens - pause and you will weep)
I think the computer has to render an image from a set range in 16M colours (24bpp) or 4B (32bpp). Then the screen screws this up with its own limits. Then the human eye interprets this as pretty low since the eye has a large dynamic range of colour and brightness.
Its a similar game with the digital cameras - firstly the image is limited by colour (24bpp), then by pixels (megapix), then by format (jpeg). Somewhere I read that 35mm film was equivalent to 12 megapixels, maybe more.. So to replace a 35mm cam we should be using 32bpp, 12megapixel cameras, with RAW format? This means big picture files.
The more bits the better, but the larger the data requirement, and more bandwidth required (HDMI v1.3) etc.