Contest: What Do the Pittsburgh Steelers and the Green Bay Packers Have in Common?

I mean beside the fact they’re both playing in the Super Bowl this Sunday, or that they’ve both won a bunch of NFL championships, or that they’ve both reached the Super Bowl in recent years as a No. 6 seed. There may be lots of other commonalities I’m not thinking of, but whoever is first to give the answer I am thinking of will get his/her choice of Freakonomics swag, which now includes the just-released Freakonomics movie DVD and a movie poster. I don’t think the question is that hard but if you end up needing a hint, I’ll give one in a followup post.