I was being a wise ass.
Ultimately, what it comes down to is feature creep.
Credit cards really took storm with the beginning of Master Charge, 60 years ago or so, and it was a way for merchants to get convenience. They gladly paid the small processing fee. It was better than bounced checks or huge tills of cash.
Over time, features creeped and fees rose. Now was once was a convenience for merchants is becoming a burden. We should have seen this coming when Discover added the cash back.
But you know what? When Discover came around sometime in the late 80s or so, it was very common for gas stations to have cash or credit prices. I would always pay cash because of this. Then the automatic pumps came along (no need to go to the clerk), and I started skipping stations that didn't have them. The pressure was on and most stations got rid of the differential, even though Discover was charging them a few basis points more, i.e. it was getting more expensive for merchants.
I guess we're going to start seeing a lot more cash/credit differences at gas stations. Some around town are starting to do it, but their credit prices are still competitive -- for now. Paying cash at a pump is a total PITA if you like to fill up.