I have heard people say that whisky never ages once you open the bottle (unlike wine, which must be consumed within a couple days, though you can extend that a bit with a fancy decanting system). I was at a whisky bar a couple years ago and the owner had a really expensive bottle that he didn't want to open. He said he wanted to sell the whole bottle -- all at once.
My initial reaction was that this was silly. How much alcohol could escape the bottle for the few seconds that it's open? But as usual, I wasn't seeing the big picture, and was thinking about whisky as if the only important chemical was alcohol. That's so superficial -- besides, isn't alcohol flavorless and odorless? Clearly you drink whisky for the flavors and smells, not the alcohol. Well speaking for myself, that's what *I* do! :-)
Over the years I have paid attention as I have opened various bottles. When I brought home my first bottle of Port Charlotte 5, even just opening the can filled the room with powerful, angry smells of peat smoke. Awesome! But those smells were very ephemeral. Today, the smells are still there, but have been greatly diminished.
So: Should you forgo opening a bottle? In my opinion: NO! Personally, I think that's the best part! I view the life of the product as a continuum, where the highly volatile components gradually step aside and make room for the middle and lower notes that can't be appreciated when the top notes are dominant.
Besides, if you don't open the bottle you have wasted your money, and the product is trapped in there and you can't ever take the journey of enjoying the product as it evolves. Note that I didn't say "ages." Aging only happens in barrels....
Christmas cake" and leather (and peat reek!) in Scotch? Heck, you might even smell freshly cut grass, which may not be tasty despite being evocative. Those chemicals are really there. Many of them are more volatile than alcohol, which means that they boil at a lower temperature. In short: If you open the bottle, they evaporate at room temperature and escape. Poof.