Google algorithm updates that effect search engine ranking position along with recent Penguin algorithm and Panda algorithm updates. Google states it is looking to continually improve search results.
W3C compliance can have a positive impact on search engine rankings. It’s fair to conclude if code works well for the visitors and browsers, it can only benefit your efforts with the search engines. So, why would one take the risk of having bad Web site code, if good Web site code will help visitors and search engine spiders alike?