Going by the track record of all previous Call of Duty game, each one managed to sell more units than its predecessor, however this time around there's no confirmation that Modern Warfare 4 will have same fate. During recent investor call, Activision stated that sales of next CoD in 2013 is expected to be down from Black Ops 2, and the reason behind this is "challenged global economy" and "the ongoing console transition,".
via N4G: pc news feed http://n4g.com/news/1173887/gta-v-vs-modern-warfare-4-battle-for-supremacy-and-billion-dollars-who-will-win
via N4G: pc news feed http://n4g.com/news/1173887/gta-v-vs-modern-warfare-4-battle-for-supremacy-and-billion-dollars-who-will-win