I'd imagine it would be better to make a new game to cater to the online crowd, instead of shoehorning a Diablo style co-op mode in.
I'm just guessing, though.
It's always something isn't it? People are making suggestions that will improve the next game in the series (if there is one) by pointing out flaws with this game. I don't give a flightpath about their dev schedule or economic situation. Obsidian are asking full price for a streamlined Dungeon Siege. People who don't feel like the title is providing the gameplay options that seem to be standard for the genre are hoping for improvements, somewhere, in this title or down the road.
You are cheerleading the streamlining and standing up for the stripped down MP. That's cool, we are all allowed to pick a side in any argument we choose but your side favors less gameplay features for the same amount of money.
People paid full price for a broken, buggy, streamlined mess of a game in Oblivion, loved it and begged for more so I don't see the problem.