Remember, this is 40-50% higher than your normal chance of getting bc. Not that women who have had abortions have a 40-50% risk. Just like other risk factors, this is a multiple of your base risk, which for women 40-49 is about 1.5%
Here are some stats re: breast cancer/abortion link:
http://www.abortionfacts.com/breast_cancer_connection/studies.asp