I don’t believe this is true, and here’s why. Yesterday I had a long chat with a clerk at my city’s main Post Office yesterday. (I was complaining about the lack of commemorative international stamps, ha ha!)
She suggested that I just use 3 “P” (permanent / domestic) stamps. When I asked how much overage that would involve, she said I would only be paying a nickel more that way. An international stamp currently has a value of $2.71. A permanent stamp is $0.92. So, $0.92 x three = $2.76. It costs merely 5 cents more to use three “P” stamps, and that way you can get a lot more variety, since they’re continually coming out with new designs for domestic use.
Anyway, I mention this because I am sure the principle would be the same with postage going to the USA. You’d need to top up a “P” stamp ($0.92) by 38 cents’ worth of stamps to get to the target value of $1.30 for a postcard to the United States.