Articles like this don't appear nearly often enough. With catalog sales accounting for 40% of all physical music sales and 64% of download sales (according to the article), you'd think that there would be a lot more ink devoted to the hows and whys behind this aspect of the music business.
The sizable, year-in and year-out sales of many twenty and thirty year-old albums lends support to my "discount theory" of music sales, that is, the notion that people will gladly pay money for albums if the price is right (as opposed to downloading them for free from file-sharing networks). Classic albums routinely go on the sale racks at large retailers like HMV as part of a "buy three discs for forty bucks" display or some numbers to that effect. It's easy to be cavalier with one's money when you're buying an twenty-year old album that you know will be great, particularly when it costs far less that a new release that you may or may not like now (or twenty years from now!). We're long past the point of baby boomers re-purchasing their old vinyl collections. People making these catalog purchases are 1) buying music that they know very well but never got around to buying, 2) finally checking out an album that they always heard was great but somehow never heard, 3) younger fans who are starting to build their collections or simply want to check out what all the fuss is about with an album that's older than they are, 4) any of the above groups of people who know that twelve or so bucks isn't a lot of money so what the hell, why not spend a bit of cash on some older music, 5) ...
It's a bit bizarre that normally bankable artists like REM and Mariah Carey don't sell many copies of their debut albums. I chalk this up to turnover of their style and fanbases. Most of REM's catalogue sounds a lot different than the music they were making in 1982. The new fans they picked up over the next ten years stuck with their newer sound, and many never looked back to investigate the older one. "Everybody Hurts" and "Losing My Religion" probably get 100 times more plays that "Radio Free Europe" on radio and VH1, so it's not too shocking that the albums containing those songs are the ones that still sell.
Mariah's career pulled an about-face when she split from Tommy Mottola and began making music for kids instead of music for adults. It's little wonder that not many of her fans care to return to the outdated style of her shlocky debut, even if it was a huge seller at the time. This notion is enforced by Mariah's bumpy career path: becoming the biggest-selling female artist ever, followed by the Glitter/psych ward/label-dropping debacle, only to stage a remarkable comeback and become bigger than ever thanks to the top-selling album of 2005. Fans seem eager to forget her past in favour of whatever she's doing at the moment, and in doing so they further distance themselves from the music she made at the beginning of her career.
Although it's worthwhile to wonder why some recent classics sell ("OK Computer", "The Soft Bulletin", Pavement re-releases) while others don't ("Loveless"), there's a much larger elephant in the room: why are AC/DC still shifting so many units? "Back In Black" might be widely known, but it's not the type of album that fans and critics (even those who are strong devotees of classic rock) would regularly rank high on "best ever" lists. And yet somehow, "Back In Black" now finds itself among the top ten best selling albums ever, and much like the similarly eye-popping sales figures for "Eagles Greatest Hits", these numbers really sneaked up on people.
Neither band ever had the Beatles/Stones/Zeppelin honour/stigma of being the "anointed band", and therefore never reached a level of overexposure and oversaturation that those bands did. When I was in high school, those were three bands that were passed down to us from our parents and were anecdotally acknowledged to be part of the musical canon that you simply had to be familiar with. AC/DC didn't have to be the greatest ever, they were simply a very good band that played balls-out rock and roll, which for 99% of the populace is far more important than who was the most influential or most innovative.