This map illustrates the gender gap in the 2008 Presidential Election. The darker the blue the larger the advantage for Obama among female voters.
In just two states, Nebraska and Arkansas, did Obama receive fewer votes from women than men. In Arizona and Utah, Obama received the same number of votes from women and men.
The gender gap, or the pro-Democratic nature of female voters, is so common that textbooks regular include a discussion of it in chapters on voting and political participation.
The real question is, why?
Women perceive the Democratic Party to be more concerned with domestic issues that regularly affect their lives (i.e. education and health care). This is contrasted with a Republican Party that cares more about inanities such as zero-based budgeting that just don't resonate with Joanne Six-Pack (Ha! that was an awful line - I promise not to use it again).
And, here's another reason. The truth of the matter is that a clear majority of women are pro-choice. As long as the GOP is a bunch of men telling women what to do with their bodies, the GOP will be on the wrong side of this gender gap.