The authors fail to mention that a J-1 visa is not only for work-and-travel programs. Highschool exchange students come here on J-1's, doctors, teachers, and many more. Work-and-travel is just a small part of J-1 program (http://j1visa.state.gov/programs).
As to the low wage being paid to workers - did the authors expect them to be paid more than a regular american worker with zero experience? That's why we have these low wage jobs where you can walk in with no experience and earn some money. There is a different work visa (H1-B) for foreigners with college education/work experience.
Most J-1's are happy to earn what they earn. Most of them do travel in the US at the end of their stay and experience the life/culture.

The authors make it look like these kids are being abused and take away jobs from the Americans, which is far from the truth.