This is so obvious to anyone that frequents this site that I seriously question your motives. Look at the top selling games this generation
-SSBB: Local and online multiplayer
-Mario Kart Wii: Local and online multiplayer
-Call of Duty 4/MW2: Local and online multiplayer
-NSMB Wii: Local multiplayer
-Halo 3: Local and online multiplayer
GoW1/2: Local and online multiplayer
See a theme? Its not just the 360. The simple fact is that games with multiplayer sell more due to more people experiencing them in social settings and going out and buying the game for themselves. This isn't even considering how multiplayer lengthens play time far beyond any single player game.
Considering you posting history I'm inclined to think your posting just to cause trouble, but I'll give you the benefit of the doubt.
The definitive evidence that video games turn people into mass murderers
