I agree. You answered Matt R's question number two with the fact that we have airbags because of big bro. My answers are:
. The point of the airbag is to stop your chest from hitting the steering coloum. If you slam your chest hard enough into the coloum, you can go into cardiac arrest or be crushed so much you can't breathe.
The seat and shoulder belts will stop you from hitting the steering column too. Maybe not at 100 mph but for most other accidents. However... 2. Every single new car since the mid 90s something has come with airbags. If they didn't help, and hurt more than they saved, then why do all cars have them.
...big bro did a study that only about 14% of people used their belts in 1986 or something so in order to protect us from ourselves we have air bags which we have to pay for whether we want them or not. 3. The injuries recieved from airbags are much less than not having one. Think of a car hitting a tree at 60mph. There is a sh!tload of momentum coming to a halt real fast. Even the seatbelt isn't going to be able to hold you all the way back. Plus, when the dash/steering wheel ends up in your lap in under a second, I'd like to have a cusion of air between it and me.
Again, this is an extreme example. The majority of accidents don't involve speeds of 60 mph (single or multicar headons) or more. If you live where I do, speeds don't get much more than 50 mph on a good day because of the traffic. And that cusion of air you desire would be supplied by properly worn belts. Look, I read that same study where Matt R's statistics came from and frankly, statistics bore me to death. And, I'm not all that moved by statistics because of how they are gathered. To me many times statistics = fuzzy math. However it was interesting to note, if we can believe the statistics, that air bags only contribute a 9% increase in protection if you are already using your belts properly. In overall injury reduction, they only contributed to a 7% increase in protection while using your belts. And using the belts is the best way to not be injured by the bags. So, in reality (to me anyway) I wear my belts not for crash protection but for protection from the air bag! And you have to keep at least a 10 inch space between the steering wheel and your breast bone. If you can't, you've got a case for an on/off switch which I wish I could get. It's interesting that my F150 defaults to air bag off for the passenger. I'd hate to be four bying and have mine discharge. 
Karl 
