As someone mentioned earlier, in all fairness, most of these actresses are models. Even if they aren't on all the catwalks around the world, Keira, Scarlett, Eva, Nicole and even Halle have had better luck with advertisements/editorials/beauty campaigns than most models have.
And you can't just say it's because of the names they lend; there are plenty of actresses out there, but it's the same ten or eleven that keep getting the fashion work.