WillowWood makes a very good point...
Why? Like you, I've witnessed it over and over again with women I know who are family friends or fellow church members, and like WW said, I believe their contentment that allows them to function so well is based off of their relationship with Christ. Of course you couldn't give that explanation for every woman as not all woman are Christians, but...I do think WW has a great point. Anyway, I'm that type of woman myself. Granted, that doesn't mean I desire to function the remainder of my lifetime without a significant other, but if it never happened...I don't think my feelings will be hurt. Honestly.
Again I'll say, though I do agree that it tends to be easier for women to function well without men (in a romantic sense, not friendship necessarily - we all need a friend a or two, male or female), I did say that it's not as common as you or others might think. But still, this type of theory should always be taken with a grain of salt anyway. Like the_patriot said, it varies from person to person because everyone is different.