According to the Scotch Whisky Association, whiskey, once bottled, is a finished product, “If you keep a 12 year old bottle for 100 years, it will always remain a 12 year old whisky.”
The reasons whiskey remains basically the same while wine changes have to do with a couple factors: tannins and alcohol content. Wine has much more tannin content than whiskey. Whiskey has no innate tannins, and only gets a small amount from the barrel in which it ages. Tannins can cause change in a bottle of wine over time, for better or worse. Whiskey has less tannins, it does not have much chance for major evolutions in flavor.
More important than tannins: alcohol content. Wines may have between 11 and 15%, or higher but almost all whiskeys are bottled at a minimum of 40% ABV. With such high alcohol content, the possibility for a dramatic chemical reaction from oxidation is much lower.
Whiskey can change at all over time, especially if it has been exposed to sunlight or temperature fluctuations.
Wine decanters are specifically designed to encourage interaction between liquid and air, always without a cap. Whiskey decanters tend to be built for stability, have glass tops, and usually have a wide bottom. Air is not a factor in whiskey decanters, because it does make much difference.
So, wine is decanted for flavor and whiskey is decanted for looks. Incidentally, do not use a lead crystal decanter, because over a long period of time it could leach into the whiskey.