I'm not saying RGB888 is perfect for human color perception, but to answer your question about why cameras can go higher than 8 bits per channel (like with .RAW files) while the display can only go to 8 bits per channel - the basic reason is because people will take the things their cameras record and put them through transforms and scalings and stuff like that. Like with James' example about his pictures in the cavern - if you take a shot where you want to take the data your camera recorded and remap it to a different output range, you are losing precision, and your output data is aliased. So if you want to be able to do levels or color remappings or other photo manipulation effects, you need the extra bits in your source, cause you are going to lose bits when you do those effects/transforms.