I am not an expert on spirits and distillation, or even on Vodka,
However I do know that vodka can start of from almost anything, potatoes, malt, wheat, rye molasses, even wood pulp.
It is distilled to it�s maximum alcohol level, which can be as high as 100% by volume, At this stage it would be same as any other alcohol, ie alcohol is alcohol is alcohol, But being pure spirit it would have the tendancy to absorb water from the atmosphere, thus finding it�s own level, at around 80to 90 % alcohol by volume, at this strength it would still be impossible to drink, so water is added to bring it down to around 40% by volume, or 70degrees proof, may well be less dilution in the soviet states,as 50 and 60 % alcohol by volume is quite common there,
Thus in a manner of speaking the only difference between one Vodka and another would be the type of water contained therein.
I hope this makes some kind of sense to you.