"It apparently was never formally in their system because the release of Arena pre-dated [the Australian Classification Board's] existence," Bethesda VP of PR and Marketing Pete Hines tells Joystiq. "This is simply an error on [the classification board's] part. It should just say PC, not multiplatform. We've notified them and they're going to fix. There is no new version of the game coming. Just a clerical mix-up."
A completely free and legal copy of Elder Scrolls: Arena is available directly from the Bethesda site.