I don't understand what reason there would be to add vodka to a cream-based pasta sauce.
Vodka is allegedly tasteless, and the alcohol burns off. So why?
Is it to make the recipe 'nouveau' or something?
First, the alcohol doesn't burn off. We had a table about the percentage of alcohol left after a period of cooking, and especially in something cooked as short as a pasta sauce, there is a substantial amount left. For the longer discussion, see Cooking away alcohol.
Second, alcohol is a great solvent. It can leach aromatics from spices and herbs which wouldn't come out with water only. There is a good reason why extracts and essences are made with alcohol. While a really good extract needs a long time, even the short cooking time will be enough for alcohol to make a difference.
Third, it can stabilize your sauce. Cream is an emulsion of fat in water, and not terribly stable, especially if some acid is present. Alcohol dissolves both fat and water, so it will stop the cream from eventual separating.
Fourth, maybe you happened to find a not so great recipe. Vodka will help with the first three points, but it is seldom a good choice for cooking, because there is almost always another alcohol which will accomplish the same and introduce a good flavor which harmonizes with the remaining ingredients. For pasta sauces this tends to be a good brandy, but it depends on what else you have in the sauce. And because even vodka will leave a taste of alcohol in the end, it is hard to argue that it can be used where the taste should be kept unchanged.
Vodka brings out some flavors from the tomatoes that can't be release with water or fat. It acts as a solvent to bring a different profile to the dish. Vodka is recommended because it usually add less other flavor than other alcohol products. If you don't want to add any other flavor, use a pure alcohol product like Everclear - or moonshine.
Vodka may have a flavour. In America and Europe, mass produced vodka is highly filtered so as to remove any impurities that might flavour it. This is ideal if you are going to use the vodka in a cocktail or such where the flavours are unwanted.
However, in traditional vodka areas of Eastern Europe and Russia, the drink is made without filtering. Thus the vodka from these regions will impart a flavour when added to your sauce. Is it possible that the recipe you are following had an Eastern European origin?