I would guess that Nike has a long running exclusivity agreement ($$$$$$) with Apple. Also there's some proprietary RF hardware in some iPods and iPhones, that devices like the FuelBand and Nike+ sneaker thingy use. Which would be impossible to do with just a software app.
Another sports manufacturer, like say Reebok, could do a similar thing, and partner with another phone-maker like Samsung. Might run into patent issues though.