That's kind of a simplistic way of thinking about business. Short-sighted. A better way is not to think just about immediate revenue, but to think about the COST of unrealized income/potential when a person leaves a site for one of those low clicks.
For example, a person who clicks on a low paying ad MAY have clicked on a much higher paying ad if they'd stayed longer.
Or, they might have bought something from you. Or they might have seen your site is great, and bookmarked it.
Do you think Wal-mart would advertise for K-Mart in their stores for a pittance?