Digital Music News has a data-heavy post on the new U2 album, No Line on the Horizon, that seeks an answer for why the album is headed for such a low first-week sales tally. The latest album is on target for 400,000 to 500,000 units, according to some estimates. That's "stirring considerable concern," wrote Paul Resnikoff, "based on a solid, mid-800,000 first-week on the previous U2 release, How to Dismantle an Atomic Bomb."

One candidate for cause of lower sales is the unsuccessful first single, "Get On Your Boots." It is not being well received by radio and it is not especially active on file-sharing networks.

There's nothing to be concerned about -- at least no more concern than is already caused by broad market changes. I have a more obvious and simple explanation for the lower first-week sales of this new album: Albums don't sell what they used to sell. That's about it. That fact can account for the entire deficit if No Line on the Horizon sells just 509,000 units. Must of the rest could be accounted for by the slow take-off of the first single.

When HTDAAB was released in November 2004, it sold 840,000 units in the U.S. in its first week of release. In terms of technology adoption and new online music services, November 2004 was a far different era. The iTunes Music Store had been open in the U.S. for less than a year and a half. Broadband penetration rates were lower than today. Tower Records still existed, and there were far more independent, regional and national chain store locations. There was no iPhone. YouTube was not the go-to destination for music discovery. Music-based video games were not selling tens of millions of units.

U.S. album sales declined 3.9% in 2005, 10% in 2006, 15% in 2007 and 14.4% in 2008. Over those four years, album sales dropped 37%. It has been roughly 4.25 years since the last U2 album. If that extra quarter-year is assigned an annual rate of loss of 15%, the total percent loss in album sales from November 2004 to February 2009 is 39.4%.

Now take that decline of 39.4% and apply it to 840,000, the first-week sales of HTDAAB. That's about 509,000. In other words, if U2's new album sells 509,000 units in its first week, it will have done nothing more than mirror the rate of decline in album sales since its last album was released. If individual track sales do modest business, even a first-week tally well under 500,000 units will generate the same trade revenue.