Really? Then how come I could play the entire SP campaign in coop with my friends online? Why would they port all that content to a new engine that changed the game not one bit aside allowing me to play over the network? The other MP modes had no discernable difference to SP aside gameplay. What was the point?
Not with GRAW on the Xbox360 you coudln't. There were some maps specifically designed for co-op, but they weren't part of the story. Also, the gameplay itself was very different in co-op, missing the cover mechanic and squad order elements that made the SP game so fresh at the time.
GRAW on the PC, on the other hand, did allow the campaign to be played in co-op. Hiwever, it was a completely different game than the 360 one which, while re-using assets from the 360, ran on a completely different engine and had a very different playstyle.