Google Adsense is one of the major source of income of Google Inc. and one of the best advertisement platform on the web. It is known for delivering relevant ads and they always work on the relevancy. They have a very restricted criteria and term of service and probably never compromise with their policy. So it is the 1st choice of webmaster and publishers. Google has recently posted a blog on their Official blog titled: “Upcoming changes in backup ad options ” has confirmed that they are going to retire Public Service Ads. In Adsense words:
we’ll gradually begin retiring public service ads (PSAs) from AdSense sites so that we can focus our efforts on developing new opportunities for these partners.
They have also written that a blank space will be appeared instead of PSA. I think instead of this google should show an image hosted by the publisher to promote some other contents of publishers choice. On the other hand they have confirmed for their Non-Profit partners that they will continue serving via Google Grants.