According to a post on their official blog googleblog.blogspot.com, they accidentally deleted their blog and the control was taken over somebody else. Thankfully for Google, the blog has been restored and back in running condition.
As visitors of Undelete My Blog Project know, accidental deletion of blogs is nothing new and it happens to the best of us, as this incident shows. I just would like Google to tell us how they restored their deleted blogs so that hapless bloggers (like yours truly!) don't have to go around digging in Google cache for it.
And by the way, I think that it takes a lot of guts to stand up and say that you made a mistake. We are only humans after all. But not many companies do that. Nice going, Google!