This is true. In fact, if you come across a merchant that accepts credit with a minimum purchase amount or tacks an extra fee, you can take the receipt and call the terminal owner (visa/MasterCard) and report it. The receipt has a terminal ID, and it turns out the likes of Visa get really pissed if merchants do that.

I know this because I used to work on a US military base. There was a sole merchant on a particular installation that was doing this, but it was extreme. They'd force you to buy over 10 USD if you wanted to use a card, and it was the only place to grab a snack. One day there terminal was shut down, and for a period they only went to cash payments. Once they took credit again they removed the minimum purchase. Turns out somebody got pissed, and reported them.

Regarding the article, the ~390 USR sounds about right to me. I only use a credit card, pay it completely off at the end of the month. I've never once paid interest since in the 8 years I have used this card. Every few years I buy a plan ticket with the rewards.