Pilots and mechanics both make what they can negotiate, especially if they are unionized. Much of the leverage for these negotiations is the principle of supply and demand as you noted. As you may have noticed, the system is set against both pilots and mechanics for getting paid well, and most pilots at major airlines still aren't making the wages (corrected for inflation) that they were making before 9/11. This principle is not isolated to the aviation field. You may have read news articles showing how CEO/executive pay has increased exponentially compared to the average Joe. The CEOs get this money in part because they have become geniuses at figuring out how to make labor work more hours for less money and benefits. Pensions have mostly gone away, employees are paying more of their health care costs, companies restructure under bankruptcy laws and convince workers to take less salary, scope is picked away at during every contract negotiation, etc.
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