Although Yahoo! does obtain its data from Google, at the present, there are differences between the Google rendition and the Yahoo! results. Yahoo! tends to display a wider range of webpages as results in comparison to Google, but allowing the user to drill down a little more than in Google. As well in my opinion, there tends to be some modification of results to favour displaying results that have some relevance to the Yahoo! directory (although I must say, this is a little difficult to determine in some instances).
source: http://microdoc-news.info/home/NewsOnGoogle/2003/07/10.html
