Some pro-choice atheists use this polling data as evidence that the pro-choice position is correct. The argument, in a nutshell, is that atheists become atheists because they are logical thinkers, and then become pro-choice for the same reason. Pro-life atheists are explained away as being still, partially, under the influence of religion.
While some people do become atheist and then become pro-choice, atheist author and Pitzer college professor Phil Zuckerman suggests that it's more commonly the other way around:
With an emphasis on seeking to make abortion illegal . . . conservative Christians have found a warm welcome within the Republican Party, which has been clear about its openness to the conservative Christian agenda. . . . What all of this has done is alienate a lot of left-leaning or politically moderate Americans from Christianity. Sociologists Michael Hout and Claude Fischer have published compelling research indicating that much of the growth of “nones” in America is largely attributable to a reaction against this increased, overt mixing of Christianity and conservative politics. The rise of irreligion has been partially related to the fact that lots of people who had weak or limited attachments to religion and were either moderate or liberal politically found themselves at odds with the conservative political agenda of the Christian right and thus reacted by severing their already somewhat weak attachment to religion.The key here is to understand that while people on the fringes are the loudest, most people don't take their religion all that seriously. People don't necessarily take their churches as authorities on moral and political issues, and where church teachings deviate from their personal views, they may leave one religion in favor of another or of none at all. (Zuckerman focuses on liberals, but I note that this works for conservatives as well; in recent years, reconsideration of same-sex marriage by church leaders has threatened schisms in the Episcopal, Methodist, and Presbyterian denominations.)
That's not to say that logical reasoning doesn't play a role in what people believe; it absolutely does. I am an atheist myself, and Christianity's unanswered questions had a lot to do with that. But the decision to publicly identify as an atheist—to lose your church community, expose yourself to scorn from the general public, and possibly damage family relationships—is a highly emotional one. And it's a lot easier to do if you already disagree with your church about abortion.
Conversely, if you've lost your faith in God but remain pro-life, and are part of a pro-life denomination,* there's less reason to publicly identify as an atheist. You might as well just remain another doubter in the pews, invisible to the pollsters.
*My own secular identification was made easier by the fact that I belonged to the Methodist Church, which disagreed with me both on abortion (pro-choice) and same-sex marriage (opposed).