Okay, this isn't strictly relevant, but it's interesting. Computers needn't be these almost invisible things we use and manipulate stuff within. The model could've been an environment which both we and the computer pour things into. The computer would then be responsible for what to do with that environment.
Instead we have the metaphor of agency where the computer pretends to be a medium instead of acting like a robot. It's quite cool, and a much deeper metaphor than any I'd previously thought about.
Quote follows, from Bridging the Gulfs: From Hypertext to Cyberspace - Thierry Bardini:
The anthropomorphization of the computer translates the user's desire for the computer's responsiveness and capacity to perform action (Laurel, 1990b, 358), two major anthropomorphic qualities of the interface implemented by the designer. Brenda Laurel (1990b, p. 358) realized that these two qualities, responsiveness and capacity to perform action, in fact "comprise the metaphor of agency," and in her defense of anthropomorphism, she stressed later (1991, p. 143) that this does not argue for the personification of the computer, but for its invisibility.