It is social cost that makes people in a MMORPG play alone together, or as that source says: "joint activities are not very prevalent, especially in the early stages of the game. WoW’s subscribers, instead of playing with other people, rely on them as an audience for their in-game performances, as an entertaining spectacle, and as a diffuse and easily accessible source of information and chitchat. For most, playing the game is therefore like being “alone together” – surrounded by others, but not necessarily actively interacting with them". By limiting yourself to social interactions which are indirect, you minimize your social cost: You don't owe anybody anything, you have no obligations, no need for loyalty. And as long as you consider the MMORPG to be "just a game", that is actually a very rational thing to do. The so-called "virtual worlds" are massively inferior to the real world in most aspects, and reserving your social capital for the real world makes total sense for most people.
But for the game this has negative consequences, both for the game company and the players. The less players are socially integrated in a game community, the easier they stop playing. And for the player who refuses to pay the social cost of belonging to a guild, large parts of the game remain out of reach, further reducing his desire to keep playing (and paying). Blizzard appears to be very much aware of this, which is why we will get the looking for raid functionality in patch 4.3. This basically lowers the social cost of raiding, and thus opens up raiding to those who were unwilling to pay that social cost before. The change of difficulty is more or less a secondary effect of trying to implement pickup raids: The current raid system simply requires a degree of organization a pickup group can't hope to achieve. If LFR succeeds it isn't because pickup raiding is "easy" (because for the individual player that isn't necessarily the case), but because the barrier to entry, the social cost is now low enough for people to be willing to try to participate in this form of end game.