Some of the small and midsize advertiser have been reducing their use of search advertising that is displayed on search engine sites.
For the past few years this method has been a great source of business for them because they reached a targeted market. But the cost per click has been rising for some of them to the point that they are spending more than they want to. As a result some of them are turning to other sources of advertising.
Some of the very big companies are now starting to devote money to search ads and are helping to drive up prices. They are taking away some business from smaller merchants.
Google isn't concerned about some of the smaller merchants who have left because what the big companies are spending more than makes up for it.
Both Google and Yahoo say that small companies with the right message and the right product can do very well with seach advertising no matter what the big companies are doing.
Here is a link to an article that contains more details about this
The Small Fry Sour On Search Ads