Duh.
Absolutely, but a big part of the wealth creation process is the person who's just doing his job and earning his pay. Since his risk and value are limited, so too, is his proportion of the reward. He is creating wealth but only indirectly, and he may view it as 'just earning a living'.
If we assume that it's earned, we assume that there's only so much available to be earned.
I disagree on your leap from first assumption to the second. Creating more wealth for one's employer certainly increases the amount that's available to be earned. Whether it takes the form of a raise, more hours, or promotion to supervising others, more business for the company should translate directly into more money available to be earned.
A capitalist economy creates wealth, allows all who wish to participate to be a part of that wealth creation, and share the rewards in proportion to the value they add.
Of course it does -- that's why it works so well. Human nature being what it is, people will respond to incentives in their own self-interest.