Payments with commissions are a managerial tool to incentivize a certain behavior, the same way there are other structures to help organizations behave in a certain way.
For example, you can incentivize people based on an easily measurable metric fully under their control (e.g. $ sales, customer support tickets solved, factory throughput, etc.), or choose to align everyone's behavior (e.g. Profits of xyz division of the company - hardly under a particular person's control).
That's the same principle behind giving CEO and other senior executives incentives based on stock options: you want them to create value and get share price up, while leaving them maximum freedom on how to get there.
Each approach has its pros and cons in terms of how easy it is to explain to employees, track the metrics, create a collaborative environment (or not), incentivize intra-company communications (or not), and the impact it has on workforce productivity (also, it depends on how you measure productivity...)
In designing an incentive plan, one has to decide which one of these factors one wants to prioritize.
Because of the salesperson role, and because of the type of mindset/profile these people predominantly have, it is easy/common to have their pay structure heavily based on commissions.
Looking at things from the other side: if you ask a salesperson about compensation structures, possibly she would be wondering why engineers' or designers' pay is not linked to sales, so (instead of working on interesting and beautiful stuff) they would prioritize shipping features that help her sell... (as an example of not so beautiful designs that sell more think about the design of certain low cost airlines websites) ...Then again, possibly, the salesperson only knows what would help her sell more easily TODAY, and not what she is going to need in a year's time... you need an engineer not directly incentivized on current sales to think about that!