The same seems to be true for very young blends (aged 3 or 5 years) bottled back in the sixties or seventies - they are almost all superb and I do not think they were all such excellent when bottled decades ago (in such a case the whisky industry would have a major quality problem today). No, it is rather likely that the different ingredients and aromas (e.g., esther) do combine and balance each other over the course of decades. This is why I rate this bottling significantly higher today than years ago (I just opened another bottle out of my stock for curiosity).
If you do not believe in bottle maturation here's another explanation option: Given all the modern style "designed" whiskies of today these old style drams are simply more distinctive / enjoyable these days compared to a time when all whiskies were "old stylish". Your choice... BTW, I bought this bottle for 67 Euro in September 2011.