Quote - A higher resolution mesh means more points to which a texture map needs to be accounted for, hence higher(and much higher) resolution Texture Maps can be used; for bigger, and higher DPI, renders. 

 

A higher resolution mesh means that curved surfaces are broken up into more, smaller facets so that curves appear smoother. 'High resolution mesh' It has nothing to do with the size (resolution) of texture you can apply to it. You can apply a higher resolution texture (ie: a texture image file having more pixels) to any mesh, high res or low res.

V4 has a lower overall vertex count than V3 because they did a good job of 'cleaning up the mesh', removing redundant edgeloops, using fewer, larger polygons wherever facetting wouldn't show. This economy allowed them to use a higher resolution mesh on the face for better extreme morphing, facial expressions etc.

V4 also has far better UVmapping than V3 (how the model skin is spread out onto a flat texture image). Important areas like the face are spread over a much larger portion of the texture map, whereas in V3 the back of the head enjoyed most of the texture and the face was a tiny area in the middle. So the same size head texture file (say 4096 pixels wide) will look far better in a really big render of V4 than a 4096 wide head texture on V3. Again, this has nothing to do with how many vertices there are in the mesh.

The "high res Jessie figure is a good example of how not to model a figure - the extremely high polygon count serves no purpose at all.