Treyarch’s Call of Duty World at War may have just been a reskinned Modern Warfare, but evidently that hasn’t stopped people from buying the map packs.
8 and a half million WaW map packs have been sold since launch, spread over 3 individual map packs.
In related news, Infinity Ward are soon to bring out the first DLC for Modern Warfare 2, which this editor suggests will become the biggest selling DLC in history. We don’t have an exact date for release yet, but it is due out in spring.