Hardly a suspect when it comes to defending anybody with Led Zep - did I ever mention here that they are overrated, Rob? - affiliations, I rule out that he had anything to do with this. The man is wealthy as hell and his solo career has carefulyy avoided commercialism (with maybe the exception of his first, still very zeppelinish solo album), he could be making even more shitloads of money in a Zep reunion, yet turns everything down and rather records duets with Alison Krauss with his voice carefully mixed into the background.
If he was the right choice for a blues festival is another matter. His blues credibility is largely based on those two Zep albums from the sixties. Since then I find that his folk and ethno influences have been the much more dominant influence on him, if anything, he's avoiding in his work to do what his old audience wants from him which is roar over blues riffs and 12-bar harmonies.
I guess the organizers wanted to make a buck with him, but Plant on his own isn't (and to his credit: doesn't want to be) the draw of a Led Zep reunion. I'm sure they were approached for the Olympics ceremony too and he refused ...
