You've got it backwards. "Without a belt, air bags are of slight benefit".[0] Airbags are chiefly a nanny measure to protect people too stupid to fasten a seatbelt.
What are you talking about? That article clearly says that air bags without seat belts are "of slight benefit", but are very effective when combined with seat belts.
[0] http://www.nytimes.com/1992/06/26/us/study-shows-air-bags-sa...