The 8 bit limitation can be important. Even if I cannot see the difference, the computer can, and more importantly, any filter or process that uses more than 8 bits can see the difference. For example, a histogram starts to look like a hair comb when you do a levels adjustment in 8 bit, or color banding, and this is mess sometimes in bump mapping, etc.

Gimp has 16 bit float, which I don't think PS has, and levels can be adjusted above and below the clipping points. This is important because the colors can be recovered.

Also, if I want to use a photograph as the basis for a texture then curves would be important, but I don't agree that curves are unimportant in map making.