But the keys given out on scratch-cards at the Blizzard Worwide Invitational event in Paris in June, and BlizzCon 2007 in Los Angeles last August, have no such restrictions. It's these that are changing hands for serious cash. Originally billed as beta keys "for an upcoming Blizzard title", Blizzard only announced that these would work for the Lich King beta once it had started.
WWI keys seem to be selling at a particular premium, perhaps because they also come with an access code for an exclusive Diablo III-themed vanity pet, Tyrael.
It's still possible to opt in to the beta test via the accounts page on the official WOW site, but access is not guaranteed. If you absolutely must play Lich King now, there's only one thing for it: check your bank balance, get out your wallet and head over to eBay.