There was a report on NPR a couple months ago, I think it was on their "Weekend Edition" show. They were talking about the Super Bowl ads, but they went into detail about how Cadillac was re-positioning itself in the marketplace, aiming for a younger market. The Led Zeppelin ads were mentioned.
Anyway, this link might give you a new angle. You'll need Real Player to listen to the story. It's worth listening to.