Gonna have to side with this. The parent poster is effectively trying to rationalize what is a technical regression by most interpretations under a veil of woo and mysticism.
I'm not sure about this specific scenario (seems to me you're right, it's technical), but this principle has been actually used before and abandoned recently. The size of the iPhone 6 is a great example of something Jobs dismissed under usability notions, despite them certainly having the technical ability to do it. Now it's done.
Although not sure if Jobs changed his mind, or if this was a "post-Jobs" decision. Apple's product development timeline would make that seem unreasonable.
Apple Watch offers a new screen to work with. Single-hand operation is still possible. It does not match the experience before for the moment, but it will get better. Viewing it as user surrounded by devices, it will offer a clearer picture.
I think voice control (Siri here) will reduce the need for another hand to get involved in operation. Actually, we could categorize all the operations. I guess for most of those high frequency operations, voice control + wrist triggered display + customized settings would be fine for many users, if they are working well. I believe Apple has fact-based analysis on this and made their choice. How that would deliver is another story.
