I would concur that atheism is not a belief system - I think we have fairly well evinced that notion. However, is atheism not a faith statement? It would seem to me that atheism is as much of a faith statement as theism.
This is why I, although I act and intuitively see myself as an atheist, am logically an agnostic. To move from agnosticism to atheist takes faith. Faith that there is no God. Personally, the belief that there is a deistic first mover who started everything off is fine by me - I don't have a problem with it from the evidence we have. Intuitively, I think atheism explains things better than deism, but I cannot rule it out.
Knowledge is a funny thing. Cogito ergo sum leaves us with only one piece of knowledge we can be epistemologically sure of: that we, individually, exist. Thus everything else becomes a game of probability, based on experience. This is how the scientific method works. But although overwhelming evidence counts as 'fact', there is always an element of doubt. There always will be. We could be living in the Matrix, after all.
As a result, I sometimes wonder whether it is wise for atheists to jump on theists who claim atheism is not a belief. In some senses, and when equated with faith, it is. It is a belief that God does not exist. I believe it. I can never prove it. I have faith that it is the case, weighing up the probability based on all the evidence at hand (inductive reasoning to arrive at a conclusion). In the same way, I believe that a teapot is not flying round the moon. Just because it is a belief in a negative does not mean it s not valid. We actually hold an infinite set of beliefs - things we believe are not the case. We only communicate a minuscule percentage of these, of which one is the belief that 'God is not the case'.