Somewhere between 1.0 and 1.5, revise.any/revise.own seem to have been connected to the ability to create a new Category in discussions. Without one of those, the user can't create a category using Create Category. But they can by creating a topic and entering a new category on the create topic page. In 1.0, neither the revise permissions were needed to create a new category. The revise permissions were never hooked up to anything I believe.