I suspected something was wrong wih the Yahoo! Canada homepage on January 12, 2010, when I read that an article would reveal one billionaire's 2010 predictions while also offering thoughts from ten of the world's wealthiest people. So does the article feature one billionaire and nine millionaires? Or maybe there are some trillionaires in there as well. I clicked to the article to find out and, in fact, it's nothing but billionaires. Therefore, the apostrophe should be after the S.