That is absolutely not their website
This is one of those things that Apple never claimed was supported, and yet there's something about that behavior that feels like such a natural intuitive implication to the technology that a lot of people feel alarmed or even cheated when they realize it's not possible (yet). It's been funny to watch the various discussion threads as people pop up talking about their shocked realization and disappointed feelings.
Update: I did realize when watching the WSJ video that the "mirrored" display actually appeared to have greater "resolution" (more pixels in height and width) than what she had on her laptop. So that's something.