Activision has made nearly $70m just by selling map packs for Call of Duty: World at War.
The three map packs have sold, as of Mid-August, 6.5m times around the world. Each pack costs $10, and now that we're in mid-October, we can presume sales are higher.
Those sums were done by Gamasutra as part of a detailed analysis of this week's NPD figures. The aim of the article was to work out how much each American spent on Call of Duty: World at War.
Over half of World at War's 11m worldwide sales were made in the US where, concluded Gamasutra, fans spent (on average) $65 on the game.
Expect Modern Warfare 2 to follow suit, then - not to mention Guitar Hero and DJ Hero.
Activision, however, is not the only publisher that understands how important DLC can be. Bethesda's best-selling RPG Fallout 3 has expanded five times through premium additions, for instance.