Lauren was awesome enough to leave an actual link to the newly released proposed changes for the DSM-V. Here's the page with Eating Disorder revisions.
One of the proposed (indeed, it's already in the DSM-IV) criterion for a diagnosis of Bulimia Nervosa is: "Self-evaluation is unduly influenced by body shape and weight."
In a diagnosis of Anorexia Nervosa, the criterion related to weight perception is: "Intense fear of gaining weight or becoming fat, even though underweight, or persistent behavior to avoid weight gain, even though underweight. Disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or persistent lack of recognition of the seriousness of the current low body weight."
As someone who's never taken even Psychology 101, and as someone who has variously been diagnosed as BN and as AN-P, what I'd like to know is: what exactly prevents the BN diagnostic criteria from mentioning an intense fear of gaining weight or becoming fat? What about "disturbance in the way in which one's body weight or shape is experienced"? The vast majority of bulimics I know have consistently reported these feelings. I know I do - almost constantly. (Side note: it blows.) The AN diagnosis doesn't apply until you're at 85% of "expected" body weight, which is vague, but which is sometimes rendered as "minimum ideal body weight" in less official writing. If I can self-report all the criteria of an AN-P diagnosis except being at 85% or lower BMI, is there really some sort of switch when I drop from 88%, to 87, to 86, to that magic number, 85%? Anecdotally, I can tell you no, absolutely not. I feel as crappy or as great (depending on the hour or day) at 90% as I do at 85%. Weight, shape, fear, and weight gain avoidance are just as persistent for me. I think I may mask the fear and disturbance better when I'm at a higher weight, but it's there. It's always there.
I'd be interested in hearing the rationale behind the differences.