In a typical company, earning a fixed monthly salary, you will end up paying the company the majority of the money you make for them, and the more value you produce the company, the less you earn by comparison (since in most companies your contribution is not immediately reflected in the salary and can be hard to measure).

Flat fee + 10% of earnings seems very, very generous to me by comparison.

But I do agree that was a very important detail left out of the article!