I think I found the main reason why models are - in general - anorexic(sp?)

It occured to me when I thought about the subject of nude (not porn!) photography. to depict a nude subject in a pleasing way there is one thing I would avoid: fat rolls. I mean the "multiple chin and guts" kind of fat rolls, not the plump kind.
In nude photography it would require a certain amount of careful posing to avoid any visible rolls even in slim models.
Then it hit me: fashion photographers got lazy and wanted models that could be photographed in any position without any fat rolls. And the only way to get this is: no fat at all. after all: most fashion shootings involve some skin and photoshop can only do so much :)

This concludes my random thought of the day :D