The 5S is the premium/flagship/prestige product.
This will be reflected in the build quality, specs and price.
This is the iPhone aimed at those who care about RAM, CPU, GPU and those that can afford luxury goods.
They may not know what a GPU is but they have the money and only want the best.
While both models appeal to the fashionable through the use of color, the 5S is for those willing to pay a premium for style.