Why different prices for cash and credit at gas stations?

Here is a pet peeve of mine.  Why is does it seem like it is only gas stations that make you pay a higher price for using credit cards?  Shouldn't that be true for all retailers? 

What the gas stations are doing here are two things.  One, they are pushing off the fees that the credit card companies charge them onto the consumer.  You didn't think that those reward points you get from your credit card company came out of thin air, did you?  Two, they are also trying to take in more cash. When they take in cash they do not necessarily have to declare the cash on their tax filings.  This is exactly what Richard Kiyosaki states in his "Rich Dad, Poor Dad" book series.  He wants everyone to run a small business, doing as much of it as possible as cash only.  This way you can run your business at a loss on paper, pay no taxes, and maybe even get assistance from the government.  Isn't that great?

I once heard of a take-out restaurant owner in a neighborhood where I worked, that did a cash only business.  A co-worker of mine said that she had seen the owner pay for groceries with food stamps, and then drive away from supermarket in a new Lincoln Continental or similar luxury car.  Anyway, we guessed that she really didn't need to be paying for groceries with food stamps.

I imagine that the gas station owners are doing a similar thing, by pushing customers to pay cash in order to save a buck.  I wonder if the Service Station Association had Kiyosaki as a guest speaker at a national convention or something.  

The bottom line is I hate to be inconvenienced so someone else can pocket more money.  There should be laws that prevent businesses for charging different prices for cash and credit payment.  While some may argue that people who want to pay cash shouldn't be penalized by credit card user's service fees, all I have to say to that is, well maybe we shouldn't have credit cards at all.  I didn't come up with this system, I only use it because it is convenient.