Online components for games have increasingly become mandatory by publishers to prevent consumers from selling their games once they are done with them.  Shooters have the easy out by implementing online deathmatch, but other genres still struggle to find a way to implement multiplayer. 

The recent Ninja Gaiden Sigma 2 did it with separate online co-op challenge modes, and it looks like perhaps God of War III may also taking that route.  The Gamer Access recently discovered a section on Sony's Retail Loyalty site covering God of War III that very specifically said the title will have co-op. 

Assuming this isn't a typo, we'd assume the co-op will be limited to the franchise's popular challenge room modes.  Game director Stig Asmussen has made it clear that they have a story to tell in God of War III, and multiplayer doesn't lend itself to that.

"I'm a huge Resident Evil fan, but I got two hours into Resident Evil 5, and I wasn't playing multiplayer, either. I stopped playing, which I've never done before. Previously, I've beaten them all." Stig explained, in an interview with GamePro. "With God of War 3, there's a story we want to tell and an experience we want to deliver, and multiplayer doesn't fit into that."

God of War III is due in March, exclusively on the PS3.