Atheism on the rise?

A BBC article says that atheism, or maybe agnosticism, is on the rise in the US.  Surprisingly they gave 9/11 as a reason people maybe more likely to be agnostic since they see terrible acts committed "for my God."  They pointed at recent bestsellers as evidence of this growing atheism:

Note that there are three times more atheist in Europe that there are in the US.  Also, Christians are still clearly a majority in the United States.