Total equity =/= Annual profit
I assume you did:
2.5 billion total equity / 293 employees
=~ 8.5 million / employee
Putting a value on Valve is a complete shot in the dark, that $2.5B is just what some analyst hit when he threw a dart at the wall.
#2 - The number of employees is those who attended the beach party from an employee guide from earlier in the year = there are more employee now.
The math here is completely arbitrary cause both the numbers used in the division are probably incorrect or just assumptions. Also keeping in mind that wikipedia isn't the best source for reference.
Apple is one of the biggest companies by market cap. They claim to create around 512,000 jobs (http://www.apple.com/about/job-creation/).
However many of those jobs are in their retail stores which their business could at least in theory do without. Also many are in manufacturing where there will increasingly be automation.
I hear a lot from politicians that we need to get people spending so that they can create jobs. However a fair amount of the economic activity that I do is via either clicking on google ads or buying games from Steam. A lot of these games are written by very small teams. So I could quite easily spend a lot of money without really creating any jobs at all.
"Although Valve’s finances are private, Michael Pachter, an analyst at Wedbush Securities, estimates that the company could be worth around $2.5 billion today."
So in truth, we don't know the company equity at all.
goldman sachs: 1.8m