I have a few guesses. I think video DACs used to ship with lookup tables, so they'd be 10-bit internally, but you could only feed them 8-bit data. SGI could a

I have a few guesses. I think video DACs used to ship with lookup tables, so they'd be 10-bit internally, but you could only feed them 8-bit data. SGI could always throw more money at things, they had expensive hardware. The DVI standard only deals with 8-bit samples. HDMI and DisplayPort support 10-bit samples, but they're newer. Most desktops used DVI for digital video until not that long ago. Software support would be a lot of work back in the day when applications drew to a single framebuffer. These days, you usually have the applications draw to dedicated buffers, and the compositor draws the screen. This makes it easier to mix 8-bit buffers with buffers of other depths. Typically, you'll want to do 10-bit with hardware support, because it's just so much faster. Software is more geared towards 8-bit or 16-bit, but GPUs will support 10-10-10-2 in a single 32-bit word. They'll also be much better at working with 16-16-16-16 or 8-8-8-8, and mixing all of them together. Then there's all the software support. (Note: I've remember editing 16-bit files in Photoshop ages ago, but they'd be displayed at 8-bit, and the main difference was reduced banding after extended processing.)