Some women are golddiggers, but more importantly, all women, as a rule, have golddigging tendency. (There are exceptions, but I am talking of a rule.) This is very well established by now.
I recommend reading David Buss's textbook, Evolutionary Psychology, 4th edition. In particular, Women's Long Term Mating Strategies, where the first heading is Preference for Economic Resources. Women consistently rate importance of economic resources in partner twice(!) higher than men. This is consistent from 1930 to today, and does not change whether most women are in the work force or not. As a textbook, it has lots of references you can check yourself.
There's a difference between gold digging and being attracted to more successful men, in that gold digging is motivated by a conscious incentive to expend the man's economic resources. Unemployed men living in their mother's basements are unattractive compared to, say, machinists, who are in turn less attractive than doctors, but it's less a matter of golddigging and more a matter of social status and respectability. There's probably diminishing returns in the range between machinist and doctor, with a step function down for unemployed slackers and a step function up for multimillionaires.
Not everyone thinks it's human nature. In fact, there's no real reason why we should think that it's human nature rather than (say) a purely social phenomenon that's entirely learnt, and can therefore be changed.
Actually, there are reasons, and lots. Go read the literature. Really.
One of the best study is International Preferences in Selecting Mates. This is a large study (N=9474) with samples from six continents, from cultures with monogamy and polygyny, etc.
there's no real reason why we should think that it's human nature rather than (say) a purely social phenomenon
No reasons except that we already know from separated twin studies that genetics plays a strong role in behavioral traits. Then also as you look at other places in the animal kingdom where learned behavior takes a greatly reduced role to wired/instinctive behavior we see many analogues. Birds provide many examples whereby the male must demonstrate his ability to provide an environment, sustenance, and protection for potential mates. Some male birds build their nests that the females examine before choosing a mate. Other birds demonstrate athletic abilities through dance.
Saying that it's just as likely that male/female behaviors are learnt as they are inborn is akin to saying that it's just as likely that having a womb to give birth with is just as likely learnt as inborn.
Male birds also wear and display decorative plumage in order to attract mates, whereas female birds tend to be more drap. Obviously it's natural for men to look and dress prettily in order to demonstrate their attractiveness to women, who as the ones being wooed don't need to put in the same kind of effort.
It's funny how selective our analogies to nature are sometimes.
You completely missed the point. The point is that there are many examples of similar behaviors that aren't learned in lower animals that don't have the ability to learn much of anything the way humans do.
Thinking up an example of a different trait attributed to the opposite sex in humans is completely irrelevant.
If you want to address this subject in a meaningful way -- rather than find a nit-pick over an analogy while obtusely missing the point, maybe you should look into refuting the mountain of twin study evidence that shows that nurture lost in the nature vs nurture debate.
A social behavior that's been around in nearly all societies in the world? Human nature came first and shaped our society, not the other way around. Anything that goes against human nature usually ends up in failure and/or many deaths (Communism, extreme socialism, etc). We need to learn to embrace it and use it to our advantage.
There was a study done sometime back at a Swedish university (I can't find the link at the moment) where they had the same mindset as you. A family raised a son and totally removed all male-oriented things from his life. They even gave him dolls to play with. He ended up gravitating towards male-centric things and they stopped the study.
I recommend reading David Buss's textbook, Evolutionary Psychology, 4th edition. In particular, Women's Long Term Mating Strategies, where the first heading is Preference for Economic Resources. Women consistently rate importance of economic resources in partner twice(!) higher than men. This is consistent from 1930 to today, and does not change whether most women are in the work force or not. As a textbook, it has lots of references you can check yourself.