This data can, as with any set of data, be interpreted more than one way. Some publishers will use it to justify continued low payment of authors on the ground that a few home runs are the only way the industry survives. Other publishers (and maybe some of the same ones!) will delve into the figures to try to discern what will sell well in 2005 and 2006, and adjust their offerings accordingly. Some will even try to divine other patterns, such as the dominance of multiple-title properties and authors; maybe we can sacrifice a goat and read its entrails to see what that really means.
One useful feature of this data, though, is that it concerns actual sales to readers. It isn't fogged by returns, or tied shipments ("If you want more than 25 copies of Dark Tower VI, you have to accept at least 5 copies of each preceding book in the series"—and those of you howling "antitrust" are far more trusting than you should be). It isn't fogged by self-reported estimates by bookstore owners. Unfortunately, neither is it fogged by figures from nonbookstores—not just Wal-Mart and Costco, but books sold in hobby shops, or at airport news stands other than WH Smith, or in grocery and drug stores or hospital gift shops, or ordered direct from the publisher, and so on. In other words, it's a useful set of data based on actual sales, but it's far from a complete picture of bookbuying in 2004—and that's before getting to those of us who buy remainders and used books, and wouldn't touch a bestseller in a bookstore (but would borrow it from the library).