This is what I use to listen to 5live on a Saturday afternoon and it illustrates my favourite feature of the iPhone and the iPod touch - the external speaker. It's so nice to be able to stick a podcast on and wonder round the house during chores with it in a shirt pocket, like a transistor radio. There are times you don't want to be wired to your device, you don't want the wires in the way, you don't want your ears blocked and you don't want to be that focused on what you're listening to. You want the sound less centre-stage. And lots of podcasts work better like that, slightly recessive in the attention in the way you'd listen to radio, rather than slapped in the middle of your head where earphones put them.
Actually, that's be a good brief for an augmented reality app, talk to me from off-stage, don't demand I stare at you the whole time.