In gaming industry “co-op” by default meant two players. Now there is a different story. Things have changed now in multiplayer gaming world. The terminology now is not different.
Infinity Ward even today believes that two players is the sweet spot for cooperative-based gameplay. Recently in an interview the director of communications of the studio, Robert Bowling said that there will be a definite change in the co-op concepts between last year’s CoD:WaW and and the MW2 that is going to be released this November. He further added that in Treyarch’s effort they can participate in four-player campaign co-op, but the new sequel of the Infinity Ward will not be featuring a campaign co-op mode at all.
He also said that in fact there will be something entirely new i.e. a two-player, specially designed Special Ops mode. He mentioned that it is “designed to be replayed over and over again.”
Let me quote Bowling: “Two player seemed to be the magic number for co-op. That’s when it stayed really fun and intense without becoming a clusterf**k of things. We just found that two-players was the most fun.”
Whatever may be happening due to too many people trying to work together in a game. What we expect is great things from the developer.