Our skin does not only reflect light directly. Some rays get into the skin, will be scattered and reflected from flesh or bones. Some rays get lost. That makes skin abit like self illuminating some sort of glow because you can see light at the skin where no light should be in some cases. When skin is thinner then you could even see the influence of blood and flesh under the skin. That changes even the color of the light rays.

I am quite sure that Oblivion has some kind of faked sss. Just look at the light sources and the lighting of the face compared with the lighting of the clothes. It is not really super realistic but it is sort of sss.