No human face or body is perfectly symmetrical. Even those that seem to be, if you mirror one side to the other the asymmetry becomes pretty apparent. Doing the same to both halves will wind up looking like two different people. Whenever you hear professional sculptors talking about realism in their sculpts they'll always tell you to break the symmetry, but it has to be subtle. That article above is a bit absurd because all it did was distort the example faces so they wind up looking like they're missing a chromosome. But if you mirror those example faces you'll see even those are not symmetrical faces.

Mesh symmetry is not the same as aesthetic symmetry. A model has to have perfectly symmetrical topology in order to mirror morphs and rigging. The asymmetry is added in after all of that to increase the believability. The Poser figure most commonly sited for asymmetrical topology is the G2 female - mostly Sydney, but she shares the same mesh with all the other G2 girls. The asymmetry in the mesh is in the chest above the breasts and along the ribs. The story is that It was done deliberately to mark the meshes to prevent piracy - moronic way to go about it imo, since it does little more than deter people from creating add-on content and breaks the model for certain features of the current Poser, like mirroring morphs.