The cognitive leap to associate moving a mouse or keyboard (in your hand) with stuff going down on a screen is significant compared to just touching something you see and it moves. The former represents how we typically interact with a computer, the later how we interact with everything else. It's actually kind of amazing that Apple made both those interaction types - Apple 2 was THE FIRST time you had a keyboard + s…
Are you shitting me?
Edit: Makes more sense with the 'affordable' qualifier though it is still debatable as a "FIRST".