They don't configure the lacrimal and eye white for sub-surface scattering, or the SSS values are set wrong. You can sort of get away with it on skin, but not these other places. And thin skin, like the eyelid - lots of SSS there too.

It is also SSS that softens the diffuse effect of bumps, i.e. small deviations in surface normal. When they use a Lambertian diffuse shader instead of SSS, it looks really wrong to have the bump depth set correctly. So people turn the bumps down, because they're using a Lambertian diffuse and they have to, otherwise the skin looks excessively dry and bumpy. But then the loss of variation in the normals adversely affects the specularity, causing it to be too even. If they notice, then they start doing specular maps, introducing variation in specular reflectivity that is not real. These maps are there to compensate for the inadvertant fakeness of the specular, due to trying to fix the fakeness of the diffuse.

The whole house of cards falls down at the slightest deviation in lighting or viewing angle.

When it's all working right, you are fooled into thinking it's a photo.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)