Understood. However, i don't think the whole "pop media culture" classification holds. I don't believe Audi was looking for that specific "pop culture icon", when organizing their marketing campaign. I think Audi was looking for a young entrepreneur, an all around media icon and one that is also recognized worldwide. Justin fit the bill, and it wouldn't have matter if he was a pop star or a tennis player.
Also, Audi has done a remarkable job of media placement in the last couple of years (in the United States) to promote their new offerings. While the car might "make it" in Europe on "it's own merits", recognizable and abundant advertising is key to having success other markets.