PTSD and post deployment illness studies

Data that are in a paper showing that 30% of Gulf veterans fulfilling published case criteria for CFS have comorbid PTSD and this latter group has the most impaired cardiovascular reactivity to stress of any among the group of vets with CFS .
(source Title: Physiological and Psychological Assessments of Persian Gulf VeteransProject: VA-5B )

My question is why does the VA tie all disorders to PTSD in the majority of it studies ? Is this to slant or color the issue ? You can read between the lines.
Jagmedic