quicko: 10% fee

Can you believe this? I went to the post office today to mail some letters home. Realizing I had a surplus of the conveniently discounted-for-December local card-only stamps, I asked about using them for my international January cards. It took me a minute to actually understand what the lady was saying. What I understood was that they cost $2.10 (this is the cost of an international January card). Hence, I wanted to use four of my $ .50 stamps and buy one $ .10 stamp. She refused and said I needed to put five $ .50 stamps on. I couldn't understand why, seeing as the cost was only $2.10. Well, in and out of circles we went until finally I realized that there is a 10% charge when you use local stamps to mail something internationally. Is this not bizarre? And pricey, relatively speaking? Whatever it is, it is very un-American. Ah, that's it: it's Australian.