I think it's called "having fun."
The point is that some friends are playing Mario together. What do people do with Mario games, they run around pointlessly having fun, ignoring the point fairly often. This is part of what makes a Mario game great, that the world and the physics are fun to explore and play around in. The co-op is less about working together (it seems) and more about having that experience together...
That being said, I just explained to myself why online isn't all that important... I'd still like it and I think Nintendo underestimate the power that this with online co-op Wii Speak would have had.
I think you took it the wrong way. I never said Mario and Luigi gang up to screw Blue Toad togetheris not fun. When I saw the videos, I was thinking how I'm gonna screw over my friends when we play this game together and the laughs we are gonna have.
However, I agree online for this game is not that important. It's nice to have but not necessary.
MikeB predicts that the PS3 will sell about 140 million units by the end of 2016 and triple the amount of 360s in the long run.