>>> This functionality should just be built into Poser's obj exporter. I don't know the reason why it isn't, why it's tied to Zbrush alone, or why it's the sole realm of 3rd party scripts/plug ins. If one python coder can figure out how to do this, and it's a vital part of a figure development workflow, why isn't this just included with Poser content creation functionality?

It has to do with Poser's breaking apart of groups at the boundaries. GoZ disregards the duplicate vertices at the boundary edges.and returns the mesh "as-is" to Poser. If you GoZ the mesh to ZBrush and then exported that OBJ from ZBrush to your desktop, you'll see that each body part is a separate OBJ instead of being welded.  As soon as you start trying to weld the duplicate vertices, it changes the vertex order.

Adding true "unimesh" support in Poser, and NOT breaking the object part into groups, would fix that.