check the man's wallet.
I mean, being a 'gold digger' is HUGE and completely realistic these days. It also does happen the other way around today, but it's just not as common for a guy to compromise looks for bank accounts.
Sociology and biology do really answer this question on a serious level, however. We, as women, are hardwired to find a suitable mate who can create and provide for a healthy family. On a chemical level, we react to indicators of success (i.e. - he'll be a breadwinner), emotional compatibility, being able to create a stable environment for our children, and whether he has the ability to be a father figure. None of those really point to physical factors, allowing us to fudge around with more ease on that aspect if we're getting a great deal on the other stuff.
Men, however, are wired to find a woman that can carry babies. Simple as that. It's no coincidence that guys are turned on by the reproductive and baby-rearing parts of our bodies. We can go ga-ga over things like hands or six packs, but when they look at our bodies? They see curves, cleanliness, etc. all as signs of fertility, along with larger breasts as a clear indicator of the ability to breast-feed. This all happens on an extremely subconscious level, but it's there.