Were you wearing a seat belt? I always thought air bags were mainly for those people that don't use seat belts.
What are the stats on seat belt alone vs seat belt and air bag vs air bag alone?
This is a very common misconception. If you notice in vehicles air bags are labeled as a 'supplement restraint system or SRS' because they are intended to supplement, not replace, the use of seat belts. Air bags are engineered to be most effective while wearing seat belts. You can google search SRS air bags and find a lot of information however these are two good places to start:
http://www.iihs.org/iihs/topics/t/airbags/topicoverview
http://www.safercar.gov/Air Bags