In the paintings or drawings of unclothed women, curvy parts of body are depicted. It is done mainly for the purpose of attracting attention of male viewers. Very often this type of depiction is meant to find the attracted eyes, and not the eyes interested in the art. I would say that these paintings have used the natural beauty of human body as an object rather using it as a subject of artistic depiction.
Take a case of one artist, Bouguereau. He was a French artist who painted human figures as realistically as possible. His paintings are known as photo realistic paintings. There is a class of artists and art lovers who believe that a realistic figurative painting would be suggestive of undesired elements, attached with corporeal desires. If we look at the paintings by Bouguereau, we would tend to go away from this belief. Main purpose of figurative painter who paints man of women cloth-less is the promotion of art and not the sensuality attached with such subjects.