I think Individual skill comes into play here also.

I have been one of two main tanks in my guild for close to a year now, and Multiboxing for almost 6 months.

Many is time, I have ran a few guildies in through an instance when they couldn't get a full group, or Boosted my own toons through instances.

Every night, I'm a solo player, Taking on Ulduar and Heroic ToC right now (solo meaning only one toon being played in the group).

As far as battlegrounds, and Arena's Haven't done much of them due to my connection. But I figure, If I had a cable connection, I would be ok at that also.

Most of my life I played semi-Pro Jazz trumpet, so as with any musical ability, there is some multi-tasking going on there.

now I am far from the best player in solo or MB, but I do well enough.

Stephen