Not for this game but for others.
When the client renders a character model, the character object is broken down into its constituent elements and rendered piece by piece. The more possible options for a particular part of the model, the more data has to be associated with it.
In our case, we can probably render the entire face as a single byte: 00000000 through 11111111 easily covers all our possible combinations of faces, horns, noses, and mouths. Probably not eyes because of the color choices and mismatch flag. So eyes we'll do separately.
I don't know off the top of my head the exact number of color choices for eyes, but it's probably in the neighborhood of 64. One byte, composed of 8 bits, can handle 2^8 values, or 256. If we assume 64 different choices for eye color, then we have 64+64 possible values with a single bit left over to manage our mismatched eyes flag.
So we have one byte handling the entire face including options not available (separate horns and face shape), and another byte just for the eyes. The limbal rings are yet another byte just to handle that. Now it's possible they've rolled them in to something else, but I doubt it as no other race really has something similar it could be taking the place of. So that's off by itself. That's what I was talking about when I said the limbal rings are more complex than the facial structure. They have to be handled separately rather than being read in all at once like the rest of the face.
Of course we're also talking about single bytes of data here. Hardly a herculean feat for any computer constructed after 1975; so the difference in processing is miniscule even on the somewhat handicapped PS3.
This wasn't a matter of processing or memory. If it were, the limbal rings wouldn't be a thing. This is a matter of SE didn't think of it.