'Differential Diagnosis' -between OCD and Eating Disorder

Hi,
I have heard that some practitioners state that individuals with eating disorders may have OCD, and that the compulsions of the OCD is what is causing the symptoms that the individual with the eating disorder experiences(many other issues would be envolved here also obviously). I've read the information on OCD in the DSM-IV Mental Disorders manual. It has a section called 'Differential Diagnosis' were they talk about Eating Disorders (Also, Paraphilias, Pathological Gambling, and Alcohol Dependence or Abuse) were they state that the difference between someone having OCD as opposed to the other disorders I've mentioned is that individuals experiencing the other disorders 'usually derive pleasure from the activity and may wish to resist it only because of its deleterious consequences' (quote).

Can anyone give me any more information relating to the above. Or is that all I need to know about the differences between OCD and the other disorders I've mentioned (were some state that they also have OCD because of their compulsive like symptom).
Thanking you in advance.
Tangerine