How highly do we value uniqueness in our RPG characters? I think we all want to be heard.
I was playing a female Draenei hunter with Evizaer even though I already have one. Same model, same professions. A few days ago, I was planning on transferring the older, level 43 hunter to our current server. I wanted to do this because she has a Nightsaber mount, the Furbolg wand, and pretty high Mining/Engineering (it's hard to keep up professions with RAF). But the rational part of my brain kicked in, and since I suspect we will only hit 48 by the time we head off to GDC Austin and then Aion, I decided against the transfer.
That Nightsaber mount is special. I remember going to the newbie Night Elf area and doing every Darnassus quest I could find. I did the same thing for a little Gnome mage I have because I don't like the appearance of the elephant nor Mechostrider mounts. But at the same time those accomplishments uniquely identify those two characters.
Achievement is also expressed though generational items, often earned during time-limited events. Wearing a Pumpkin Head in FFXI said "I was there". FFXI is without a doubt a much more social game than WoW. Players had casual clothing that they would wear in town. I had a very clownish costume of a Pumpkin Head, a blue kimono, and white slacks which I would often substitute with a Rusty Subligar. Here is an example of how ridiculous I often made myself look with the subligar.
It was a statement. Among all the Hume Dark Knights with face/hair model #3, I was the guy who wouldn't wear pants. I was also a walking trophy shelf. I never did any end game raiding in FFXI; event gear was all that I could show off.
In WoW 1.x, standing around in IF with all my fancy raid gear was enough to set me apart. Even if I did manage to obtain clown gear, I dare not remove the trophies of my accomplishments. During guild raids, I wasn't that unique snowflake anymore; everyone had uber gear. Thus I frequently brought "toys" from all the holiday events: snowballs, moon beams, pets, a reindeer, etc.. I often had at least one application of Noggenfogger on me at all times. It still is my favorite item in WoW. I made Evizaer come with me to Tanaris just to do that one quest.
The synthesis of social and competitive aspects cannot be decoupled. Your accomplishments mean nothing unless compared to others. Has a friend ever been really excited to tell you some feat he completed in a game you've never played? Sure you feel happy for his success, but you don't know how grand the accomplishment really is. We even juxtapose our solo trials. I can win Civilization 4 on the hardest difficulty (yea right!), but unless I've failed on Deity before, I have no sense of victory. It's all relative, just like any metric. I see players walking around in WoW with epic gear. It could be from some 5-man heroic or from Yogg+0 or whatever the kids are killing these days--I have no idea; the trophies are wasted on me.
If we use evolution to explain human behavior, the competitive backbone of society isn't that far fetched. Time and time again economists, anthropologists, and psychologists have tested the premise that humans should rationally choose the objectively better option when dealing with choices. But time and time again, humans show they would rather be better off relative to their neighbors. Keeping up with the Joneses. Or Ensidia.
Social players and achievement players are two sides of the same coin.