To me pro choice pro life is a moral choice and certainly in Britain I cannot think of anyone who would base their political allegiance around this issue.
I realise of course that in the US this is different I suspect mainly to do with how your government works with the 3 branches and the Supreme Court system of the President picking the justices etc and the Federal and States law way it works.
Though all of this said I still find it strange it just goes to show how and where you are bought up and in what system does affect how you behave and think, the nurture and nature thing but that is another subject all of its own.
To clarify the above though my position I would say is pro-life very similar to what GWB would say so some pro-lifers may disagree that I am pro-life.
On the other hand Obama, Kennedy, and others on the left voted against Judge Roberts because he was pro-life, yet they don't see the hypocrisy in their one issue vote.