There's quite a bit of news around the Internet about one billion digital tracks already selling in the U.S. this year. This LA Times post talks about the Nielsen SoundScan data and has a lovely, multi-colored chart.

The most interesting aspect of the chart is the ability to calculate the Top 200's share of total downloads over the last five years. Here they are:

• 2004: 16.54%
• 2005: 17.39%
• 2006: 18.62%
• 2007: 18.39%
• 2008: 17.68%

If I had to guess, I would say the Top 200 share is for each year's "to date" Top 200. That means there were many more songs that were at one time in the Top 200 that are not being included. If you count the once-popular songs that are not in the year's cumulative Top 200, their share would be far greater than the 17% or 18% listed. In my opinion, such a measure would be a better way to think the degree to which the more popular tracks represent total purchases.

Anyhow, you should not the Top 200 took an greater share of purchases in 2005 and 2006 but has just a slightly smaller share in the last two years (but still more than a one-point edge over the 2004 share). Feel free to interpret this as you wish in context of "the long tail."