There are images, such as toolbarbutton-dropdown-arrow-XPVista7.png which are really the same as the "default" variant. Found so far: searchbar-dropdown-arrow-XP.png toolbarbutton-dropdown-arrow-XPVista7.png Also the same are: Toolbar-lunaSilver.png Toolbar-aero.png Toolbar-XP.png Toolbar.png (allthough a little bit less dark than the above).
None of said images are perfect duplicates, but I agree we should re-evaluate which are really needed. Some of the differences are extremely subtle.
Closing this old bug that started with the premise that these images are duplicates, which they aren't. We'll just remove all XP-specific images once we've dropped support (bug 1130266).