I thing that vertices of condlines control points should not be normally shown, especially those of primitives. They could be useful only in special condline mode, they are annoying otherwise. As you can see in this example it is next to impossible to choose the right vertice to draw an edge line at the base of the cylinder when the zoom level is low enough to see both ends...
http://forums.ldraw.org/file.php/24/2184/cpvertices.jpg
http://forums.ldraw.org/file.php/24/2184/cpvertices.jpg