I just don't believe this per head thing, I know solo people that make nice gold without a doubt, but on average I would have to say that most single box people have horrid time saving money and they earn gold in dailies and that's about it. They also miss out on a lot of loot comparitively. These are people that need to buy gold because they couldn't afford cold weather flying or a raid slot.

There has to be something in machining instances, looting caster cloth on your shaman without a qq'fest, not running an instance and getting nothing but some quail and cloth, having purchasing power to buy mats when you need it, etc.

i just leveled a team, when they hit 58 some of them had just silly gear on cloak for dead mines quest and what not. I just went into hellfire and grinded quests and did the instances. Did I loot upgrades, likely I dunno. Most of the time I just click sellfish and move on. What drops is what drops, the time spent being able to loot elites is just more. The solo player just isn't doing that. Sure they can knock out gathering quests and get raid slots.