In my country, Apple didn't start selling the cellular version until now with the 7.Feel free to check the specs of them on Apple's site: https://support.apple.com/en-us/HT204507
The only difference between the Nike version and the equivalent regular version is "with Nike logo" on the ceramic back.
Was your wife's S5 a cellular version vs. your Nike GPS version maybe?
Back when I bought the watches, the Apple site in my country did show the information as I am detailing. I checked after the conversations with Apple support. But this information is no longer available. Right now I can only find the US site, like the one you are posting. So I cannot prove what I am saying.