Oh, there are plenty of all-in-one PCs out there. The problem is that I wish the PC would be in the keyboard (or better, just a lump in the power cord) and not in the screen!
(Shades of the C64!).
Vic-20, or TRS-80, I think you mean.
Anyway, how about in the monitor? And I don't mean the Moniputor; there are plenty of modern LCD based systems which the whole system is built onto the back of the LCD. Some even include the keyboard; but those are pretty lousy. Also, I'm not referring to laptop/tablet/etc, but rather industrial designs.