I see what you're getting at, and I agree that it feels quite clunky....now. But I wouldn't be so dismissive quite yet. What if in the future you could detach your screen and keep it on the table? Now, you have an actual "surface" (just like a tablet). You can play games with others on this surface . Maybe, divide the screens and then have everyone use part of their screen for their own work. (I'm just listing what I could think of doing with a really large tablet)

My point is simply that once we have touchscreens on every desktop, it might enable ways to interact with your computer that we might not even have thought of yet.

edit: added "similarity to tablet" part