When I click on your link the top entry says:

    The second largest desert is the Arctic,
    with 13.7 million square km.  The third
    largest desert in the world is the more
    familiar Sahara, with a total size of
    9.1 million square km.  Antarctica is
    the coldest, windiest, and most isolated
    continent on Earth.

That clearly implies that Antarctica is the largest desert. It's then accompanied by an image showing a map of Antarctica.

Why are you saying that Google doesn't know what the largest desert is? It clearly does - it's Antarctica.