Toyota Corolla: Poor smell

Shortly after we purchased two Corollas in 2008 we became aware of a "rotten egg smell" from both while driving and worse on stopping. Toyota told us that the smell was a by-product of unleaded petrol and to use the recirculation fan at all times to reduce the odor in the car, and to use high quality fuel. The problem continues and has been reported to the dealer at each service who was to advise Toyota of our problem. So far we've had no response. Is this the case with all vehicles using unleaded fuel, or just ours?