SERP Yahoo variation
 

One of the major differences between Yahoo! and Google is the keyword density tolerance. Google tolerates a maximum of 3% keyword density while Yahoo! around 5-6%. Now, the question is: are you going to ignore Google and start optimizing for Yahoo!? If you go over the 3% keyword density boundary Google might penalize your website, considering it keyword stuffed. Are you going to take that risk for higher rankings in Yahoo?! Certainly not. Then what could you do to "score" in both search engines? The Yahoo! search algorithm is language based so it will recognize your words and reward your website for its variety. This way you'll add a few more searchable keywords to your content and this might bring good results in Google too.