Ok so all of the other Expansion Packs say (PC/Mac) after the name, and this one doesn't! Will Blizzard be moving away from hybrid discs on this release or is it just a glitch on Amazon's part? Amazon, if it's also Mac compatible like the rest of the game, please say so! :)
Ah yes. I was tired at the time of writing, but i guess it still kind of answers his question where it says "available simultaneously", but you could argue simultaneously means two different sets of discs/DVDs. But it is the client that matters as the build of the client is what determines what systems it runs on, and you'd need the same client on all discs i would of thought.
I believe Amazon has now corrected this error on their site however.
World of Warcraft: The Wrath of the Lich King Expansion Pack (PC/Mac)