With games like WoW so aggressively balancing classes to be interchangeable in groups and able to enjoyably solo the entire range of levels, the drive to form tight-knit groups among players who complement one another well (both in terms of class mechanics to make the group work in the first place, and the playstyle and personality to keep a group together for future runs) shrinks. Granted, the old days of not being able to get a group or find a suitable solo spot on a given evening was a bitch -- but then again, there are other games for those times.