Why is important to optimise sites for Bing + Yahoo

EVERYBODY in the SEO world tells you to optimize for google. But bing + yahoo now is half of google, according June 2010 Comscore data http://www.comscore.com/Press_Events/Press_Releases/2008/07/Top_US_Search_Engines Google 60%, Bing + yahoo – 30% And since august 2010, yahoo will use the Bing search engine. Conclusion: if you want traffic, you better start optimize for Bing also. Is also much cheaper then in the crowded google optimisation...