http://martinkronicle.com/2010/06/21/trend-followers-the-widowmaker/ read the comment at the end of the article by michael. this is an good topic for discussion if anyone's interested.
Refiners are heavily owned by hedge funds, so if the markets turn down, they get out and kill the stocks. On the other hand, many of the long-term growth stocks (like CMG or BIDU) which are owned by mutual funds have held up pretty well.