They're only announcing the iOS software launch tomorrow.
I think since iOS 7 is so new, they'll test out the software on known devices and seeing what kind of glitches or things to be improved upon once users update before they release anything hardware related.
It makes sense, especially since this is an entirely different user interface than any of the other iOS versions.
It wouldn't make sense for Apple to release a new software and a new hardware line before testing it out on known products first. My guess is iPhone 5S or whatever will come next year.