I read somewhere that he even programs on paper and punches it into a computer when he's done.

As for myself, I definitely understand the problem he's describing. I catch all my fleeting thoughts with a keyboard, but I always find my mind wandering into tangents and end up losing the focus of what I'm really getting at, or I end up in a cycle of endless micro revisions. When I started writing with pen and paper it enforced a certain economy into my writing process. By having a natural speed limiter, I have to focus more on the heart of what I'm getting at; being in the zone writing with pen and paper feels totally different to me than writing on a keyboard, you get into a much deeper state of focus.