This explains some of it:
'In 1982, Atari was owned by Warner Communications, which happened to own a pair of other companies, DC Comics, and the Franklin Mint.'
The perfect associations for something like that, connecting the comics as well as the prizes, to the game itself.
Ernest Cline was influenced by this in writing 'Ready Player One' .
Seems like now it could be a huge money maker for any large game developer, maybe with not quite as expensive of prizes. All the connections to the game would sell I should think, as long as they contained clues. Or a 'golden ticket' :)
Anyways, here's the article-
(But you can get the Harry Potter version from The Nobel Collection, which is pretty sweet! :)