"Oxidation", or more accurately, "flavor changes due to air exposure" is a spectre that has haunted me lately. For years I've been a strong and sure-minded proponent of the idea that "whiskey don't change, even when opened". I have a relatively large collection of tasteable (i.e., open and available for tasting) examples. I am proud to have been able to provide real-time first-hand taste experiences to many who would otherwise never have such an opportunity. But now, like a reformed alcoholic or a jilted lover, I have difficulty understanding how I ever felt that way. Marvin, one of my best friends (two, really if you include his wife -- and bourbonhead extraordinaire -- Evelyn) could (and has, actually) teach a course on just the range of changes a good bourbon will go through sitting in your glass for an hour or two. As Barturtle said, there are layers upon layers of congeners that make up the flavor part of our favorite alcohol beverage, and the better the bourbon the more distinctive those congeners are. Each has its own rate of... well, some call it oxidation but that's only part of it. Mostly its just EVAPORATION. They're all alcohols, after all, and different ones evaporate at different rates. Whichever's most domininant at a given time will affect the aroma. It stands to reason that whatever's affecting the aroma at a particular time, that one's just about ready to LEAVE the flavor profile. That makes the one that was obscured up to now the new dominant flavor. And so it goes, all the way to... well, Evelyn noted that the very BEST bourbons are still cranking out some absolutely wonderful aromas the next morning, while the cloudy goop in the bottom of the glass looks anything but attractive.
So what's my point? It's that, if the flavor of a glass of bourbon changes noticeably after five minutes in your glass (and it does), then it absolutely MUST change at least somewhat every time you replace the layer of air covering it in the bottle. And, while it may take years for it to actually taste "bad", it probably doesn't taste accurately like the original product even by the second or third time the bottle is opened. I have a feeling that the whiskey begins to taste "off" about the time that the level of air in the bottle is such that it allows evaporation of most the "good" congeners and the first of the "nasties" becomes dominant. It's the same in your glass; at some point the whiskey tastes like Barleycorn-poop, and when that happens with your bottle, you generally just dump it (maybe we shouldn't? More research here is needed). And five minutes later it's back to wonderful again.
I'm disappointed that the flavor changes. My orientation has always been toward the history of the spirit, not (not entirely, at least) in the end-consumer flavor; and my faith in that has become irreparably destroyed, I'm afraid. The whiskey's still good, of course. Like Chuck says, you can, with care, maintain a delicious beverage for years. I would think that the nitrogen-replaces-oxygen system would be a big help, especially when combined with positive seal closures. Those work with wine and there's no reason to think they wouldn't with whiskey. I may very well begin using them myself; although it's pretty costly for 450+ examples, and I think it would be enough to use just the positive seal closures to keep overpressure in the bottle. That should discourage evaporation.
As always, though, whatever method you use... ANYTHING you do that allows actual, physical, TASTING of America's most important contribution to products that humans consume, is a major improvement over the museum concept of allowing people to gaze upon the pretty amber liquid in an otherwise untouchable bottle on a shelf.