This is interesting! basically because Google has devalued the site in some way, the brand search term is up for grabs until Google fixes it....
They've been buying loads of off-topic links, probably just pushed it too far and G is teaching them a lesson, I suspect they will be back up fairly soon.
I think they will return too in time. It's ironic that they remove them from organic results but keep them in Google Adwords, don't you think? Teaches them a lesson, and forces them into more ppc = google makes more money. What a business model.