"Any attempt to focus the lens with the lens barrel requires the distance from the film plane to the subject increase." - That's exactly what happens when the subject, in this case a piece of film, is at a fixed distance from the front of the lens. The whole assembly moves as the helicoid is focussed, and therefore the image-plane to subject distance alters. However, the requirement for a change in distance is only true for unit-focussing lenses. Most AF lenses use internal focussing, which changes the lens focal length, and therefore the conjugate focii, with only a small change in lens length. Whatever the lens construction; In practise it's far more controllable to adjust the focus using the lens than to shuffle the distance of the film-holder backwards and forwards. If only because touching the film holder has a risk of rotating or shifting the film laterally. "The epiphany is that digital cameras routinely match or exceed the resolution of Nikon film scanners" - This is an epiphany to whom? Someone that's been stranded on a desert island for the last 5 years or so?