Australia, since the introduction of the GST in 2000, has issued two different categories of postage stamps. International stamps, on which no GST is paid, are distinguished from the normal domestic stamps, whose prise includes GST. Australia Post also has a tradition of celebrating sport and particular sports success in its products, such as this label celebrating the Sydney Swans' Premiership in 2005. In fact, there has been a stamp issued for every Australian gold medal won at a recent summer or winter Olympic Games.
Considering this, it makes some sense that a stamp would be issued to celebrate Australia regaining the Ashes from England last December. It was quite a victory after the shock of the close loss in 2005. However, I have to wonder about the decision to make one of the two stamps an international stamp. Now it is being stuck on letters sent not within Australia, but to England, as well as places where nearly noone has heard of the Ashes. It looks like they're just trying to rub the 5-0 loss in to the English. Then again, why not?