I'm not sure IT is their core competence.
I'm not sure that's true. Strong marketing for sure, but I think they're more akin to Apple in this regard.
Where (to use Steve Jobs' comparison) Pepsi's core competency is marketing (they rarely put out "new" products, so revenue is driven almost entirely by marketing), Nike's core competency is probably more apparel (specifically athletic) design - since, essentially, every new thing they release is a new product, and they release a lot of new things.
My impression is that Nike apparel is designed to support the brand, not the athlete.
Either way, I'm not sure that it points to marketing as a core competence over apparel design (though it may point the focus of the design away from the athlete).