It does better each year than the past because there's more people buying?I never did understand how Call of Duty sets records every single year. How is it able to beat it's own records every year?
As time goes on there's a wider available audience, the games can appeal to more players (updated graphics, voice acting, etc.), and an individual series often has more exposure.
A Link To The Past sold ~4.5 million.
Link's Awakening sold ~6 million.
Ocarina Of Time sold ~7.6 million.
Of course, as the Zelda series shows, if you change too much about a game or restrict the platform, people won't be as interested. Twilight Princess sold a respectable 7.1 million, Spirit Tracks only sold 2.6 million.
CoD doesn't suffer from this, as they seem intent on sticking to the same proven (in terms of sales) gameplay.