Not to mention plenty of things in real life have a secondary cost. When you fly you have to pay for your ticket and snacks or extra baggage. When you go a sports event you have to pay for your ticket and food even if you are a season ticket holder (and have subscribed). When you buy a car you have to pay for satellite radio, gas, insurance, and extras for your car.
Having a cash shop isn't being taken advantage of because you aren't forced to buy it. If you think a cash shop that is 100% optional is being fleeced or taken advantage of then you need to examine your own mentality because that is the actual problem here.