It might just be my state or store, but most products do, in fact, include a price per item or prize per unit of weight or volume in very small print on the price labels.
I'm guessing this was introduced as a law, in good faith to help consumers make more informed decisions, but I doubt the majority of numerically challenged consumers take advantage of this information.
For example, all pricing labels in-store will have prices like the following, from their weekly ad: