Tactile feedback.
Hitting something with a hammer, you FEEL how hard you hit it and how far you've driven the nail in.
touching the screen doesn't give you that.
If a 3d display can fix THIS, then it'll be the new thing. But right now, keyboard and mouse offer tactile feedback, and the touchscreen does not. a 3d space where you wave your arms around? If it's anything like the Kinect I tried, it won't do.