There isn't really much you have to do to be religious either. As far as things go for my religiousness, I feel I have even less weight or things I need to do. Why ever be an atheist anyway? That's going above and beyond, giving it a title and decrying religiousness. I'd say the only people who fit under what your definition are those with no needed title religious or atheist, that are just going about life.
Well, the only reason anyone would say they are Atheist is because someone asked them what their religion is. At that point there is a division among atheists; half of them will say they are Christian or spiritual although they are not to simply avoid discussing religion, the other half will say they are atheist because they are so upset with religion they dont want to be seen as a part of it. And that division comes from personal experience with each atheist. Do you ever see atheists running around preaching to people or asking people, "Do you not believe in God?" Never. Atheists bother the least number of people and are predisposed to not ask personal questions and purposefully cause disruptions. I think there is a connection between religious/non-religious affiliation and personality traits.