Perhaps this is unique to myself, but I have found that I can function amazingly well digesting something through Audio and working on something visually. I have no formal neuroscience education, but perhaps it's something to do with how the brain (or perhaps just my brain) processes various inputs and outputs.
http://en.wikipedia.org/wiki/Lateralization_of_brain_functio...
As a secondary note to the author of this app. What a great idea! I really like where you guys are going with this. I do find it hard to listen to as the narrator still sounds like a robot. But I'm sure with enough time this will be solved as well.
I figured that it was because coding, or writing something like this comment, uses the speech center of my brain, as does the incoming audio stream. Music doesn't have any adverse affects on my ability to code or write comments, since I don't really pay attention to any of the vocals that may be present.
A recent article on audiobooks (in the New Yorker, I think?) cited studies saying that audiobook readers had markedly better recall of physical descriptions in books, presumably because the visual processing centers of the brain aren't occupied with the task of reading itself.