I agree, this is the "5S" as it's been termed, essentially a 5 re-engineered in a less expensive casing and probably a few other places to cut some costs. Considering how obviously scalable iOS 7's UI is, I would expect these leaks are being controlled to hide the existence of a larger, next-gen iPhone "6" which will launch simultaneously. Then the lineup would consist of a 4.x"* high-end iPhone in black and white with a 4" mid-range available in a spectrum of colours.
* For some math, 720p at the existing 326 ppi would make a 4.5" screen.
Well, I'm still not 100% convinced these are real, but if they are, the best theory I can come up with, that closest fits the available facts (so far) IMO is this:
This isn't the "iPhone lite" because it doesn't make sense to differentiate two products and have the new one be "lesser" than the regular iPhone. It also isn't the iPhone 5s, because it's too different from the iPhone 5 in every way not to have it's own name.
This is actually just the "iPhone" (late 2013), and what we've been thinking of and imagining as the "iPhone 5s", is instead the "iPhone Pro" (late 2013).
This year could mark the year that Apple switches to the same model as all of it's other products and stops the numbering altogether. Each year the iPhone and the iPhone Pro would be updated just like the MacBook and the MacBook pro. The regular one is cheap, sold off contract and shoveled out the door. The "Pro" model is super slim and made out of aluminium blah, blah, blah, etc. just like every other Apple "Pro" product. That way the only thing with numbers is the OS, and the phones are designated by production dates instead, just like all the other stuff they make. There is no iPhone 6, 7, etc. in this scenario and never will be.
So far, based on the available evidence, this is what makes the most sense to me.