Advertisers don't have to bid high to be shown particularly on your site and that's not how it works.
The bid price in AdWords affects how often the ad will be shown, but that does not mean it will affect you directly.
Many advertisers target specific users, therefore expensive ad will only be shown if you have that kind users (traffic).
Some of my AdSense clicks are $10, but I do not focus on the click price, but the CPM. When I check the stats among ad networks that I run Adsense most of the times at the very bottom of the list even with $10 clicks.