Why add Vodka to Stock? The recipe for brown veal stock in Modernist Cuisine (Volume 2, page 300) lists Vodka as an ingredient. Why? 

I have never seen Vodka as an ingredient before for stock, in no professional cooking literature. No alcohol other than wine. Do you think it makes a positive difference, taste-wise?

Would an author of a cookbook add ingredients to a recipe not for taste but to appear clever? (I could imagine it with this book)

Addition 1:
Very good answers so far, thank you! So far I learned that theoretically it could make a difference. But in practice? Can anyone testify to having personally, clearly tasted a positive difference in taste due to the addition of Vodka?
Pure alcohol is a solvent: that is: it will dissolve other chemicals more easily than water.  If you put vodka in oak barrels for long enough, it'll turn into bourbon as it will dissolve and concentrate the taste of the oak.

The same thing is happening while you're making stock:


The oils in whatever the recipe of your stock calls for will dissolve more easily in alcohol than water.
It speeds up the creation of the stock
You could use any alcohol, but if you would use Bourbon the stock would get a smoky oak taste, so by using vodka (which is 40 Vol% of alcohol in water) no extra taste gets added except what's in your stock recipe.
As alcohol has a much lower boiling point than water, the vodka will extract the oils and mostly evaporate so depending on the amount used it might be safe for children too if you follow the Halal rules but you should know a water-ethanol mixture forms an azeotrope.