Another reason that I can see for marking the Day of the Shoah, is that it is most relevant on a personal level to so many of us who have either lost people in the Holocaust or knew people who were survivors. Before anyone jumps down my throat, we are all supposed to mourn the Churban as if it happened yesterday, and I am sure many of us do cry bitterly as we read Kinos. In fact, there was a non-Jewish King who chanced to pass by a shul on Tisha B’av and was extremely moved when he found out that the kehillah was crying for the Churban, soemthing which had happened centuries prior to this. So it is incumbent upon us to feel likewise a sense of deep mourning that will not be healed until yemos hamoshiach.
But it is much easier to relate and mourn on a personal level to a tragedy that has occurred in our own generation, or that of our parents. And I think that’s why it is not out of line to recognize the Shoah for the devastation that it caused to people of our own time.