To create confusion and prevent markets from comparing the relative values of their offerings!

Indeed, BMW (and all manufacturers) all spend quite a bit of time creating the illusion of differences- take the term "Sport" that BMW throws around. It can be as superficial as different wheels, window trim and a steering wheel. But the marketing literature leads you to believe it has something to do with suspensions! In some models it does, in others not- all with the express purpose of making BMW more money.