I think it's more because when they were originally designed, they were supposed to be capable of going upside down. I remember watching a special about coasters "America Screams" hosted by Vincent Price. On the show, they showed a working scale model suspened track with a corkscrew in it. Unfortunatly, during later tesing phases, they realized that suspendeds cant reiliably go upside down, however the cars were all ready made. Additionally, the safety restraint release mechanism has to be on the top of the cars to let people out in the station.