Nike has had a close relationship with Apple for some time and the chances are that it's in the know about what's planned for the upcoming iPhone 5S.
Or at least the very fact that the thing exists after the not-yet-existent device was name checked on Nike's online store. It's still there if you want to go check it out for yourselves.
In the description for the Nike E2 Prime Performance training arm band it states that it's compatible with the iPhone 5 "and iPhone 5s". We're pretty sure that "5s" isn't the plural of iPhone 5, even with the small s. So go figure.
This could just be Nike jumping the gun based on expectations and the company may not know as much as it's letting on.
But given that the two have been paired up for Nike+iPod for quite some time now, we expect Nike to be making its mark on the new iPhone too.