I haven't read this entire thread, but here is some insider information:
Many years ago I worked in the production side of a distiller that producted two vodkas, one a well-known premium brand and the other a cheapie brand. There was a very significant taste difference between the two. Both vodkas were both produced from the same raw products-the major difference was the filtering process used.
Charcoal filtering was a major step in the vodka production.