I would like to remind of their "drop in/drop out" system. You come to your friend, take a second gamepad and - voilą - you play a game. Do you expect them to check your fingertips and decide "Ok, so this guy is playing now, let's search for his savegame"? I don't.
Co-op mode as I perceive it just allows anybody to join your game instantly and leave your game instantly without any importing/exporting windows.
Surely you must be joking? I sign into a gamer profile, I join. A small menu pops up in the bottom corner where my HUD will be that shows my available characters, I pick one, voila, I'm in. Sacred 2 did it for crying out loud, and that game was held together with duct tape.
Serioulsy, your post boils down to "Do you expect them to do what a bunch of others have done and is now largely considered a standard feature for this type of game? I don't".