There's always room for improvement.
Its been my experiance in the 7 years I've been running web sites (and 20 years of retail customer service experiance) that people form an opinion of your site based on the links they click that appear on your site. I believe there is a direct relationship. If you have your site set up to maximize revenue, well then good for you and I wish you the best in your future endeavors. If you are a webmaster who puts a lot of thought to your site based on its content and your visitors experiance, then I think its something to consider.
Decision making - My site is set to direct visitors directly to items of interest and individual products. I monitor the links that appear in the Google ads regularly. New ads that catch my interest I investigate for content. If its not something I would authorize as a link myself, I'll filter it out.
Doing that opens up a few issues - Yes, I am filtering out higher paying links. Its the cost of maintaining quality content. It also gives lower paying ads (hopefully more relevant content) the chance to appear. I believe that these lower paying ads will receive a benefit from the exposure, hopefully selling more of their product. Thus they see a benefit in being an advertiser with Google AdSense. That builds a relationship to advertise for a longer period of time and may be willing to pay out more per click. Eventually paying out more per click.
So is everybody happy? - Advertisers promoting relevant content get exposure. You and Google get quality links and hopefully higher revenue. I say hopefully because its quite possible that the advertisers may stay at their current bid levels thus not spending more per click. Some may argue that filtering our higher paying ads will dilute the payout per click. That may occur. However I do know that companies that have a product to sell and are succeeding as an advertiser with AdSense will catch the attention of their competitors. The nature of business being what it is, I believe that's when the bidding war starts. So now you have two or more quality companies bidding for placement.
Having said that, I will still have quality links on my site which in the long term creates a positive visitor experiance. That means a more popular site and higher traffic volume. Webmasters know that higher traffic volume is a key goal.
Rose colored glasses? - Some may say that is like looking at the world through "rose colored glasses". That may be but I think long term while building my site. I've been making decisions on link content long before Google started AdSense. To quote Google, "...our Google AdSense program to deliver ads relevant to the content on their sites, improving their ability to generate revenue and enhancing the experience for their users."(1) So its about relevancy, enhancing visitor experiance and improving, not maximizing, your ability to earn revenue.
Responsibility as a marketer - As a marketer for many companies, AdSense being one of them, I firmly believe there's a relationship between myself, Google and the product being advertised. In my opinion, Google's job is to provide the base service and provide general relevant content and this is achieved by the highest bidder gets the highest placement. It's up to me, the marketer of their service to ensure the content is most relevant for my site. Some may say that is micro-managing and takes too much time. I believe its time well spent.
So what's Google's responsility? I have a high traffic site and I play an active role in what ads appear in the AdSense boxes. There are times when filtering content diminishes the appearance of ads. For a large rectangle box that shows 4 ads, maybe only 2-3 ads appear. If that continued, I would have to reconsider the size, repositioning or removal of the ad. Google obviously would not want to see that happen. It then becomes their responsiblity to see what can be done to improve their service to increase the relevency of their display boxes. That can only be done through feedback from webmasters. The result being new beta tests to improve the service. Something that is now occuring.
When Google launched their AdSense campaign, I bet they knew they had a hot idea that would make money. I'm almost certain too that they did not sit back and wait for the money to roll in. Knowing full well that only through evolution breeds continued success. Which leads back to my initial remark...
There's always room for improvement.
**Opinions above are my own and not that of any other company mentioned.
(2)I indicate Yahoo and eBay only as examples to keep within this thread. I am not indicating all eBay and Yahoo sites are low quality links.