"Call of Duty is by far the largest console franchise of this generation," said Activision CEO Bobby Kotick as part of the announcement – a very, very accurate assessment. "And in the last 12 months, Call of Duty: Black Ops 2, including its digital content, generated more revenues than any other console game ever has in a single year. Although it is too early to assess sell-through for Call of Duty: Ghosts, it's launching at a time when the franchise has never been more popular."
The billion dollar mark was likely chosen to contrast the game's accomplishment with that of Grand Theft Auto 5, which sold $1 billion to consumers in three days, where as Call of Duty shipped a billion dollars worth of game to retail stores. Call of Duty: Ghosts was the "most pre-ordered" game at GameStop this year.