Earlier quoted context omitted.
Companies don't try to maximize total profit, but rather return on invested capital.
This can't possibly be right. Why would you forego making extra money to keep your statistical average up? What are you getting from the average number? Your theory predicts that price discrimination can't happen because companies would rather sell M widgets at X price than sell M widgets at X price and N widgets at Y price.
Why would you invest $250K for a year's pay of an employee for $0 return. You can invest that $250K in a CD for 2% and get $5,000.
Shareholders are going to have no interest (long term) having companies invest their capital in the form of cash on the balance sheet at below market rates. Hence dividends or buybacks if they can't demonstrate sufficient roic on internal projects.
You can back into a target revenue/employee by looking at risk free rate of return + equity premium (say 7%), net margin (35% for FB this Q), and say if an avg employee earns $250K .... then they'd want a bit less than $800K/employee (35/100 * x >= 250k + (.07 * 250k)).
I don't think your comparison to widgets holds up. Would a company invest capital in more production capacity to sell more widgets at zero margin (all else being equal)? No, they'd distribute it to shareholders so they could invest it in bonds or other companies, and that's the analogy.