A hesitant player base
Analysts and naysayers have been predicting the inevitable decline of "Call of Duty" for years, but "Ghosts" is the title that might actually slow its monumental pace. Most gamers will not be inclined to buy "Ghosts" twice, so they will face a stark decision: Buy it on day one for a current-gen system, or wait for the next-gen versions.
If any significant chunk of gamers elects to wait, the franchise will hit the $1 billion mark considerably more slowly than its predecessors (but it still will). Inevitably, some gamers who decide to wait will later change their minds and not buy the game at all. Naturally, PC gamers will have no trouble deciding which version to buy, but PC gamers account for only a small portion of "Call of Duty" fans.
Since multiplayer is one of the biggest draws in "Call of Duty," if players find their friends split across multiple consoles, they may not buy the game, either. You may know that players on an Xbox 360 cannot compete with players on the PS3, but the Xbox 360 and PS3 will also have totally separate multiplayer servers from the Xbox One and PS4 versions.
Barring some kind of major catastrophe, the game will probably still do exceptionally well, but the moment "Call of Duty" stops being an ever-growing cash cow is the moment that it stops being a trend in gaming. The series could continue to slow down until it becomes just another ordinary title in Activision's lineup, or even to the point where annual releases lose more money than they earn.
Another alternative is that Hirshberg is right, and this blip in pre-order numbers is simply because of the transition to the next-gen consoles. If that's the case, then 2014's "Call of Duty" installment could jump right back to "Black Ops 2" numbers — save for the fact that far fewer people will own Xbox Ones and PS4s in 2014 than own Xbox 360s and PS3s today.
The enormous successes of "Modern Warfare 3" and "Black Ops 2" owe as much to the ubiquity of current-gen consoles as they do to their appealing game design and effective marketing. "Next-gen hesitation" may not hurt "Call of Duty" as a popular series, but if the series shrinks instead of grows for the first time, it will be the beginning of the end as far as its dominance of gaming culture is concerned.