I think it used to indicate that there is no term that is 100% accurate when it comes to describing the emotions involved in supporting a woman’s right to control her own reproductive system. It indicates that the person who is saying Pro-Abortion is inaccurate “too” recognizes that this term is used to cast a negative light and are unwilling to accept that term to describe how they feel.
I would surmise that someone who is against abortion as an option would be more likely to use the term Pro-abortion as it has a more negative connotation than Pro-choice. Same reason they would choose to refer to themselves as Anti-abortion instead of Anti-choice.
Same goes for someone who has the opposite view, they are going to choose the more positive term for themselves and negative term for their opponents.
From a personal perspective I would say Pro-Choice is MORE accurate than Pro-Abortion. It indicates that while you may not personally choose that option you feel that people should have a choice. Pro-abortion seems to indicate feelings that everyone should have one regardless of their beliefs.