I have no idea what it has to do with Si v Ni, either, except that to me, Si (and Ne) types seem to make better multi-taskers due to less immersion. But I think what you're saying is really interesting for Se v Ni and that it's a difference that looks like a similarity. (Although the 'I like to read/hear stories' thing is pretty un-related to anything and more of a personal preference.) Ok, what I mean is, when my dad (LSI) and I are working next to each other, superficially, we 'look' alike: very deeply involved in whatever we're doing. However, even though from the outside it looks the same, what's happening cognitively is very different.
He is 'concentrating' in that he is choosing to block out everything except what he is focusing on. I, on the other hand, am not choosing to block things out through my sheer powers of concentration, I simply lose awareness. It's like this: I've noticed with Se-creatives, you can walk up to them and talk at them and they simply won't hear what you're saying because they're focused, but they're also not easily startled. You talk at them and they just say 'hmm', blocking you out, and then when they're done, they turn and say: 'you were talking to me?' For me, that could never happen. I cannot chose what I am aware of or unaware of. Between noticing you and not noticing you, there will actually be a 'disconnect' -- so when someone comes up to me and starts talking at me, between me noticing and not noticing is actually a moment of 'omg, why are you next to me?!' (Er, my jumpiness in this respect probably has something to do with Si PoLR and my 'acting out my shock' probably has something to do with Fe-leading and performing my reaction for others, but I think the point still stands.) When you're talking about reading a book whilst walking, or listening to an audiobook, you're still talking about something which is sensorily present which you are focusing upon, the very opposite of being an Ni space-cadet.