Unfortunately I cannot recall the name of the illusion, so finding a video of the illusion properly executed is proving to be a difficult task. I'll keep searching and post back if I find one. The actual optical illusion is quite mesmerizing, truly amazing, I could stare at it for hours.
They ARE two separate rings balancing on top of each other, albeit attached, that isn't the illusion part, at least not the cool illusion achieve when this is properly executed. I guess I understand what you are describing, the seinfeld video shows that, you could think that the rings/tires are rotating at a different speed then they are spinning. That is not the actual cool optical illusion that the spinning stacked rings is famous for though, or the illusion i was referring to when i made my tip. The superman video kinda shows it because the rings are thin, but with only two rings the full optical illusion isn't realized. when you stack sick or so think rings and the angles are precise on them, and you rotate them, you get to see the actual optical illusion trick which is quite neat.