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My point here, again, is the pupil material zone serves no purpose at all.

Well it does if one intends on rendering it outside of Poser- in my case, I would want to have it there so I can make it transparent, or use a transparency map on it to make a soft transition in transparency from the iris inward. Of course I could simply make a new mat group if I wanted to, easily enough.
If there is a material group for the pupil, it can still have the Iris texture applied to it - assuming it's UV mapped that way of course.
But if it's simply not there, then people are stuck with using a texture map on it and don't have any options for using separate maps on it unless they make their own new group, and I'm sure a whole lot of Poser users have no idea how to do that, so I can't see any good reason  to remove it.

As long as the UVs for the iris and the pupil are consistent in size, it would be relatively easy to make good textures and trans maps for achieving the fade effect to make it look more real.