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as i mentioned before, i literally can't think of any situation where the second scenario might work for lips and their surrounding area.  if it makes it easier for SaintFox to create textures, that's really great. i think that's really important to support developers, especially for a non-DAZ figure. but i've had to spend a minimum of 2 hours postworking the neck and shoulders of just about every texture i've ever used, and i can totally understand why head and body might be handled that way.  conversely, i can think of literally zero situations in which it would be beneficial to have a visible difference in detail between lips and their surrounding area, and in no situation could the lips need detail their surrounding area didn't because they render right next to each other. 

I understand exactly what you're saying, and as I've said several times in this thread over the past month or so, I have mixed feelings about the lips.
My argument  for having them separate is that with a large texture you can get some serious detail in there along the lines of spec and bump. Now if you just use photos and paste them on in Photoshop, it might not be that big of a deal, but (also as I've said several times already), when I set out on this I wanted to create UVs that would be developer friendly but also 2D and 3D painting friendly. Think "one pixel brush" in Photoshop or Painter or Deep Paint 3D or BodyPaint 3D.

But I also agree with you too, and there are definite benefits to doing it your way as well.

However, the main difference is, problems with texturing the face and lips the way I have UVd them can be overcome more easily than problems created the other way around. In other words, you can shrink down your lip map and massage it in Photoshop to make the resolution match up, but the only way to get extreme detail into it is to have a lot of texture space. Once it's small it can't be enlarged without pixellation, but something too big can be made smaller, so the way I did it is the lesser of two evils, as I see it.

Without doing the math and just guessing, if the lips were part of the face UVs and sized proportionally, even if the face took up an entire 0-1 space, that would probably be around 10% of the available texture space, maybe less. So you would have to use an 8K map just to get a high res face close up, or else risk pixellation. Most Poser users aren't going to be interested in 8K maps. That would add huge amounts to a texture pack download, and would exceed the limit of a freebie hosted here.
So with even a 4K map, you're limited even further in render resolution in a close up.

But yeah, why should it matter to have extreme detail in the lips, while the immediately surrounding face doesn't benefit from that same resolution increase? Well for one it seems to me that in a lot of photos of real people there often does seem to be more detail in the lips - more noticeable features. Which becomes even more evident in fashion models where they may have lip gloss and such, while their faces are powdered into looking very smooth and un-detailed.
Then again, as I said before, it has to be one way or the other, and to me this way was the lesser of two evils.
And also of course, if the developers are happy, I'm happy. :-)