Right, but you're inherently defining "good looking" in a sexual way. A man ass holds true to the same basic aesthetic qualities as a woman ass (symmetry and so forth), but you find woman ass more pleasing to the eye due to a more primal sexual connection. When applied to rasterized polygon virtual asses, doesn't that seem more than a little weird?
May as well say the same for any drawing, painting, or whatever else of a "good looking in a sexual way" visual.
If someone painted a picture of [insert currently-popular hot chick here], would it be pleasing in a sexual way even though it's only a painting of the actual woman? Probably.