The ulterior motive is actually that cash transactions are not traceable, so the government can't tax you as easily, and they can't keep track of your spending as readily.
While waiting for my washing:
First had this in Mexico, worked in the city where it's brewed (Monterrey). The Mexicans tend to refer to certain things in the diminutive, so this could be ordered as a "negrita", as in "Dos negritas por favor!"