I'm amazed at the feedback this sentence is generating :-)
Actually, I'm glad the level of readership contains people at the technical level to provide this explanation. You're right, of course, but I was trying to present a simple analogy for those uninterested in the deeper technical details. Many readers aren't this technical, but I agree that things should be accurately represented.
Thanks for pointing this out.
Perhaps I should have written something more like "In fact, the GUI you're used to seeing (windows, mouse, graphics) is just one way of manipulating your machine. Terminal is another, somtimes more direct route."
Thanks to all for the feedback!