Most Apple applications distributed over the web now come as zip (rarer), or dmg (disk image -- more common). Both are natively supported. Microsoft is one of the laggers in still distributing things with the old compression formats. So you shouldn't see it too much, although it's good to have Stuffit around. I think MS recently released something...maybe the latest MSN Messenger, and actually used a disk image, so perhaps things are changing. 🙂