I think the marketing differentiation works best when it is driven by factors that are hard to measure and control, but that are perceived as high value, like flavour and style. When buying bottled water, the water is free, you're buying the bottle, the refrigeration, then real-estate & inventory space, and you can compare it on those dimensions, but if you are sensitive to the taste that can override the other factors. With cola it is much much stronger because the taste is more intense and your body is conditioned to link it to the sugar and caffeine hitting the bloodstream which gives you that immediate Pavlovian response. But taking something low-cost and using human psychology to assign a high value is how marketing makes profit. As opposed to the prosaic side of marketing where you're just letting people know you exist.