I know they pass the fee onto the merchant... I don't see what your point is? Usually they tell you what the CC surcharge is and that you will pay it...
They don't run off that, they run off people paying stupidly high interest because they don't pay it out on time. In fact they probably make an absolute fortune off that... They also bank on the fact that people are more likely to buy if there is a line of credit available...
Its a tool that can be very powerful but also very destructive. If you misuse a credit card you will get bitten but if you use it properly you can purchase things that you need now. For example, if our washer blew up tomorrow we would not have any money to buy a new one AT THIS TIME because we're saving like mad for a wedding and paying for the car. But we could buy one on a credit or store card and then pay it back in the coming weeks (and save a little less this month). But we'd get the item, get it going and then pay it back as soon as we get time. You pay more for the ability to have it now. That's how loans and credit work...