"We've updated AdSense to now vary the number of text ads that appear in a given ad unit. When we have a set of highly relevant and useful ads, we give them more of a presence in the ad unit by eliminating other ads. In some cases, if we determine a particular ad performs extremely well on a page, we'll remove all other ads from the unit and show just this single ad."
"When we tested this feature, we saw that the increased user attention to these relevant ads resulted in a higher CTR. This means more revenue for publishers."
"Definitely. The better-performing ads are more useful to users and this new feature gives them more presence in the ad unit. We are very careful to consider the user benefits with every feature so we can help our publishers grow their repeat traffic by showing more useful links on their pages."