Not sure where it was mentioned, but this was something that stuck out to me, was the idea that MMO's have moved away from the idea of playing WITH other people to a system where you play ALONGSIDE other people, and I think that really touches on a great point, and what would be one of the defining cultural shifts in MMO's.
Personally, I have always hated the idea of forced grouping, it reeked of being gamey and unrealistic, and on top of that, it always ended up putting me in a situation where all too often I would end up having to deal with people I didn't care for just to get the loot that was locked behind this Forced Grouping content.
However, when I first played GW2, it showed me something grand, that players could alongside each other, that we could all be working towards an objective, and even work together and help each other get it, without needing to hitched at the hip in a group.
Now, playing alongside other players is by far the more fluid way to play a game, no need to have this formal group, to just get things done and help each other out, I think however, the main problem with MMO's is that they are not really tapping into how to make this shine better, which is why I think so many players get confused about what to do in an MMO, and cry about needing group content.
Egotism is the anesthetic that dullens the pain of stupidity, this is why when I try to beat my head against the stupidity of other people, I only hurt myself.