I am of two opinions on this. First, I think the cost of the storage may have gone down enough for Apple to up the storage and not the price (or at least not that much -- if they drop 16GB from the 5S offering). With higher quality pictures and videos being able to be taken from the device, more storage space would be required.
However, they may end up keeping it at 64GB capped (at least for now) in hopes to entice people to subscribe to iTunes Match where they can have access to their entire iTunes library from their phone. That could lure the iPod classic customers to the iPhone, but not really towards the iPod Touch.
In my own personal opinion, given their history with storage on previous phones, it would make sense to bump it up eventually, but also from what I know of business (which I will admit is not very much) it may also make sense to keep storage semi-limited to encourage sales of their other services.
For instance, I have 64GB on my iPhone and thanks to iTunes Match, Podcasts, and Spotify, I hardly have made a dent in my storage. It goes without saying that I will most likely be getting the 32GB iPhone 5S when it is available.