[chaecuna]

Wings3D: only closed surfaces, open surfaces done with a ugly trick (transparent material).

Yes, because it uses a winged-edge data structure. This keeps the models manifold/watertight, and reduces the likelihood of stray edges and un-welded vertices. The transparent material is used simply to hide parts of the mesh from the user. It does not mean that you have to export models with these hidden/transparent faces. You can use the selection tools to export any part of your mesh (export selected).
If Wings only worked the way you are implying it would be useless for making morphs in Poser. I find it works very well (once you have adjusted the import/export scaling to accommodate Poser's unusual scale).