I don't think this is a valid assumption. I know lot of "hardcore" gamers who are less socially active in real life but are very "socially" active in game world. These are your hard core raiders, guild leader types etc.
I don't agree - but there are exceptions. I'm not saying they're not going to interact with people as much as a socially active individual, but the interaction will not be based on a desire to be social - but rather a desire to achieve something within the game. That's been my experience, anyway.
They're usually focused on the "game" and not the social interaction, as in they will want to progress their character and will generally be less tolerant of players who hold them back.
A socially active individual will tend to focus on the social interaction - and will not be as focused on the game and progression.
Obviously, this is a generalization - but in the grand scheme of things, I'm quite certain it's not far from the truth.
Personally, I'm sort of a hybrid. When playing with friends - I'm focused on social interaction - but when playing with strangers, I tend to focus on the game. I don't really care to make friends with strangers that I'll never meet, but I will never be unfriendly unless they're asking for it. Also, I'm not a selfish person - so I would never put my own progression ahead of someone I was questing with. I always make sure they have everything they need before I start focusing on myself. Which is probably why I tend to solo when there are no friends online - because I generally feel other people are holding me back when I'm focusing on the game.
Also, I don't react well if people don't treat others (including myself) with respect. In fact, I can be extremely harsh if someone is not behaving in a social setting. I've got a very low tolerance for assholes and unfortunately, all MMOs have got their share.
I do agree its very hard task to balance group and solo play but I would think a MMO can favour group play without penalising the solo play. Let me give an example. In WoW you ended up competing with other players for harvesting nodes. Many people didn't like this. They hated the sight of other players despite the social dynamics that brought. So In GW2 they made it so that each player get their own copy of the node. What they should have done is, each person get a copy of the node but instead if they decided to group and harvest the same node, they get more loot than if they harvested their own individual copy. This way you can reward group play without penalising solo play.
We don't agree about what penalising means, in that case.
If you get a progression/power related advantage by grouping - then you're penalising the solo player.
Maybe they should have made gathering faster the more players on the node at a time, but still have a set limit of resources pr. node. That way, you're not giving more to group players - you're just adding a mild convenience.
I'm ok with giving grouped players XP bonuses as well, because I don't see leveling faster as much of an advantage. In fact, I tend to think of it as a disadvantage - because you're going to see less low-level content if you level faster.
That's the kind of incentive I can go along with - but never give grouped players a big advantage. I certainly don't think that's the way to go about it.