What that image suggests is that the analog audio cannot be transferred through the new Dock Connector alone! It requires the headphone jack output in addition to the new Dock Connector to go to the old Dock Connector. Either:
1. No more audio through the new Dock Connector. That would be terrible.
2. Digital "optical" audio through the new Dock Connector. Wouldn't that be a big improvement?
3. Still analog through new Dock Connector, but they decided to make it take the headphone jack too for some reason. Maybe just for physical stability?
The blogger showed how possibly the headphone jack could be integrated into the adapter design. We really don't know anything at this point on what Apple's choices are on that. This is my take.
Even if Apple integrated digital audio which I assume and hope - and I'm pretty sure it's not optical due to energy efficiency and the space the optical components would need - it would not be backwards compatible and an adapter would be easiest to use the headphone jack to loop the audio stream. The reason a conversion inside the adapter is senseless is because non-digital audio would already loose the quality enhancement and then you could as well grab it from the headphone jack. In other words: It's cheaper with the same result.