In my experience, those polls tend use questions that are very poorly worded from the standpoint of the irreligious.

For example, I remember one question that went something along the lines of, 'do you believe that something controls all that happens in the universe'. Since I think that everything that happens is ultimately the result of physics, I had to answer "yes", despite the fact that it might cause researchers to think that I was 'an atheist that believed in god'.