Actually, there was part of the book that I didn't quote which also goes on to mention that there is a type of breast cancer that a mammogram can detect that a regular exam cannot, Ductal carcinoma in situ, that is non invasive and rarely needs treatment. Read here:
http://cllr.me/NcE
Here is a PDF of the article that explains the cost benefit more clearly.
http://www.psychologicalscience.org/..._2_article.pdf