This is pretty solid evidence that CFS is not psychosomatic, given the difference in response between the control group and the group that received treatment. In case anyone was still unsure.
That said, a psychological / psychosomatic component wouldn't undermine its legitimacy in any way. Thankfully, I think we are entering an era in which psychological aspects of ailments are recognized as critical, beyond the control of the patient (e.g. not reflecting a lack of virtue or wherewithal on their part), and treatable.