Well there is some cultural variation - and certainly in cultures where women routinely go topless, breasts are not a major sexual attractor - but there are also some consistencies, such as the 7-10 waist-hip ratio being considered the most attractive. Some cultures think 28-40 is best, some 35-50, some fashionistas may like 21-30... but none find a belly bigger than hips attractive.
"Cultural variation" is like saying some hoodrats are okay with tattoos and the intelligentsia don't care for them. That all goes out the window when a naked Halle Berry with a tramp stamp is beckoning you to "hang out". Oh you don't like tats, sure, does it really matter in this case?
EDIT: Just to placate Pundit, in gaming terms someone with an 18 CHA (COM if we're using that stat) is beyond reproach. Even with a hefty negative reaction penalty, they're still going to illicit a very positive reaction.
S'mon - I'm not sure if you're disagreeing with me at all. I agree that there is some cultural variation along with some consistencies. I mentioned clear skin and symmetry of features for this - you cited waist-to-hip ratio. I hadn't read previously about waist-to-hip ratio, but yes, it looks like between 0.6 and 0.8 is preferred from what I read.
(ref) As far as I know, it is similar with breasts. I suspect no culture prefers complete absence of breasts -- but there are varying ideas on what is too small and what is too big. Even within our own culture, there is a lot of variation in breast size of the most popular models and celebrities. From back in the days of flappers in the 1920s through to the present, many small-chested women have been seen as highly attractive.
Regarding a Comeliness stat -- I think there is far more agreement about who has a 9 or lower Comeliness cross-culturally, but little agreement about who is an 18. Asymmetry, blotchy skin, and apparently wrong waist-to-hip ratio are always turn-offs. But who has an 18 versus a 14 is the subject of much more disagreement especially between varying cultures. And reaction to nudity is very culturally dependent. In some cultures, seeing a woman topless or even fully nude is no big deal, since it happens all the time. In some cultures, women are almost always completely covered from head to toe, and showing any skin is erotic.