During the 1980s, the stereotype for Japanese women was that they wanted three things in a marriage partner: high education, high salary, and a tall man.
These days, Japanese women are content with things that aren't nearly so sky-high. For marriage partners, they're fine with "average".
In Japanese, "sankou" (三高), or what would be localized as 3-Hs in English, referred to "high education" (高学歴), "high income" (高収入), and a man of "tall height" (高身長). This attitude became emblematic of 1980s Japan, when the bubble economy was in full swing.
Now that salaries and attitudes have come back to earth, Japanese women have, too.
According to Japanese TV program Mr. Sunday (via 2ch), some of today's females are "sanpei jyoshi" (三平女子), or, localized into English, 3-As women. They want partners with "an average income" (平均的な年収), "an average appearance" (平凡な外見), and "a tranquil or alleviating personality" (平穏な性格).
Part of what seemed to make some of the woman content with "average" was that they could supplement things like income by working themselves. Thus, there is less reliance on a sole breadwinner.
Many of these women came of age as the bubble was bursting—which is why they might put less emphasis on things like money. During the 1980s—and for much of the 1990s—the country seemed enraptured in greed. During the bubble era, there were stories of people hailing cabs by holding out ¥10,000 bills (around US$100). Cash flowed freely.
Of course, some people in Japan still throw around money, but nowhere near the insanity that the 1980s saw.
It wasn't just the bubble economy's collapse, however. The global economy crisis of 2007 and 2008 and the March 11 earthquake also see to fuel this desire to place less importance on transient things.
This isn't a group of women "selling themselves short". Rather, it's a group of women putting more importance on things like stability and calm. You know, things that really matter.