I think the remnants of 'Persia' officially became 'Iran' in the 1930's when the Shah had it changed. So, I would imagine for older people, Persia would come more easily to the tongue, and how other people would still think of it. In 'Oklahoma', the '40s musical, set in the earlier 1900s, Ali Hakim is described as a 'Persian peddlar' (although this may merely have been part of his peddlar's mystique: 'exotic foreign treasures' etc). In the movie, he was played by Eddie Albert.