Soft Determinism, Hard Determinism, Necessitarianism, Fatalism...Huh?

[Mudhammam]

So as an atheist, it seems that I am logically committed to naturalism/materialism. As a materialist, I must be committed to some form of determinism. On these points I think many atheists (especially today's science popularizers- Krauss, Dawkins, Dennett, Harris, etc.) would find agreement. The difficulty I am finding is understanding the discernible difference between the following philosophies, the finer points atheists seem to disagree upon from time to time. For those perhaps not fully acquainted with each view, I've provided brief Wiki definitions. Can someone please explain to me how soft determinism is not logically reducible to necessaritism (or fatalism)? It seems like a slippery slope to me...is there a stop-gap somewhere that doesn't appeal to some mysterious agency or hidden variable? If the principle of causality is essential to our Universe (as a logical principle, an algorithm, of matter in motion), could the Universe actually have been any other way (down to me presently writing this)?
Soft determinism (compatiblism)- "The belief that free will and determinism are compatible ideas, and that it is possible to believe both without being logically inconsistent."
Hard determinsm- "A view on free will which holds that determinism is true, and that it is incompatible with free will, and, therefore, that free will does not exist."
Necessitarianism- "A metaphysical principle that denies all mere possibility; there is exactly one way for the world to be."
Fatalism- "A philosophical doctrine stressing the subjugation of all events or actions to fate."