I think that your front airbags are deployed when the sensors under your hood activate. And they activate only when your front end deforms in a crash.
The "roll" sensors have to do with your side-curtain airbags if you have them.
Airbags have nothing to do with accelerometers. In some highend cars (Mercedes S-class or Lexus LS430), accelerometers are installed to predict an impending accident. When this happens, front seats become more upright, sunroof closes, doors lock, etc.. However, front airbags have nothing to do with these sensors.