Well I am. I'm agnostic about everything, the truth is, I accept (as you do I'd guess) that there is nothing which we can know for certain. Therefore, God et al may exist, but as no evidence for such a being has yet to reach me - I do not exist. I do not know what the objective reality is, I only have what is the best knowledge I have at the time, to form my conception of reality. As far as I know, there are no Blue lions in Africa, so, at the moment - that is truth. However of course, it could always change, there could be a blue lion in africa - but only in the light of new evidence.
I don't think any 'serious' atheists believe that we can be 100% certain that God does not exist. We're just, as you put it before, a much more cynical agnostic