It's a standard sort of thing. The idea is that a non-manager has minimal ability to affect the company's bottom line. While those further up have the ability

It's a standard sort of thing. The idea is that a non-manager has minimal ability to affect the company's bottom line. While those further up have the ability (and now have the incentive) to affect the profit of their division or the whole company. So a worker gets 100k with a 10% bonus, his boss gets $120k with a 40 percent bonus etc. In a good year the boss will get almost twice the worker but in a bad year he will make just 20% more.