Pretty hard to compare two vastly different arenas like that. In space flight even mature platforms have a 1%-10% failure rate.
Because of the physics involved, rockets operate at the very edge of the capabilities of the rocket. Modern auto's don't have this issue: you can drive at highway speeds all day long without stressing the materials in your engine anywhere close to the edge of the operating envelope. In short, from an engineering perspective car's aren't hard any longer.
