But then, I think using dead celebrities in ads is pretty much always offensive (unless they give consent while they're living, which has never happened as far as I know).
With this celebrity ad, there is the usual borrowed interest that doesn't really connect to the product. What Audi is saying here — in the indirect communication technique of "creative" advertising — is that the new 560PS RS 6 Avant (snappy name, that) may not appear as powerful as other powerful cars, but in fact, is much more powerful than those other alluded-to powerful cars. I doubt that that is true, but they're not really making a claim, so good luck with your future lawsuit.
But what really makes this a bad ad is that Audi isn't just exploiting a celebrity character to sell auto "power," it's exploiting Christopher Reeve, the man. Because you can't help but think of Reeve and his too-recent horrific injury/death when you see the ad. And it makes me sick to my stomach to see Audi's logo over Reeve's beautiful face.
I've emailed the responsible ad agency inquiring as to whose permission they had to get to use Reeve in the ad.
Ad agency: BBH, London.