An agnostic may range from half believing to not sure, to being almost completely certain
that there isn't any God but allows that they simply don't 100% know.
By this definition which is only ever used by believers Dawkins is not an atheist. In fact by this definition I have never encountered an atheist.
To repeat myself....
The crux of the matter is not the degree of certainty. Atheism is more of a passive or negative position, "disbelief in god" rather than a positive "there is no god" position.
Most people are either believers, or as Dawkins said they "believe in belief".
Atheists just go a bit further and say something like, "I don't believe in god due to lack of evidence and I don't think belief or faith is a virtue I am missing out on".
Agnosticism is usually reserved for somebody who thinks the question is unknowable. An agnostic reserves all judgement about whether or not there is a god - an atheist does not. Just becasue somebody like myself allows for the extremely tiny possibility that a supernatural being exists does not make me an agnostic. Its not as if I think its 50:50.
The word atheism needs to allow for some spectrum of certainty just as faith does. To me it simply means without (belief in) god.
However when I say "there is no god" there would be an implied, "subject to the vanishingly small possibility of, as yet unknown, evidence to the contrary".