btw, using two verticies in one spot is realy usefull for changing the distribution of light when you are using a smooth setting or subsurf setting.  

however, i am unsure why you need to see these lines in edit mode,  usualy its much more logical to hide them as that would increase the fps of the view which is much more important when you have multiple high poly objects in the scen which need editing.   just like in a game, when you have 400 spheres lined up like i did in my array picture,  editing the scene will become slower on the graphics card.  to improve this rather than clicking slow draw, click fast draw like 5 times.  each time you click it decreases the number of verticies displayed.   

if you like you can see this effect by adding a grid (100X100), setting it to dupliverts, and making it a parent to a sphere.