The difference that jtp and others overlook is that as horrific as Rwanda, the Russian extermination, the "Killing Fields" of Cambodia and all other such atrocities and true crimes against humanity are, as compared to the "Shoah" is that they were one time events. By that I do not intend to diminish the inhumane (to mild a word) effects such actions had on the populations, of which, we can't begin to imagine. But, they weren't systematic attempts at exterminating a single race of people that has lasted for millenia.
The Jewish "problem" wasn't one confined by the electrified, barb wire fences of Aushwitz, Buchenwald, Dachau and all the others. No, it's a matter of fact that history is replete with such attempts to permanently destroy the Jews, beginning with the Egyptians, continuing with the Persians, Romans, and Muslims, not to mention the Crusaders and all the others. It, of course continues today with the Iranian led goal to remove them "from the face of the Earth", a la Ahmadinejad.
The Israeli National Motto is "Never Again" (לעולם לא עוד) and appropriately so.