Not just Jews were killed. A lot of people who were judged to be inferior because of heritage, skin colour, disabilities, political views, or simply being part of the resistance were killed as well. The Germans committed unspeakable acts, and yet you'll be hard pressed to find a European that actually hates Germans. My grandparents lived through the war, but they didn't hate Germans. You don't need an apology to be able to forgive.
Besides, most people that actually committed those acts are dead or on their way out anyways. You shouldn't keep the son responsible for the actions of his father, or in this case, the actions of his great-grandfather.
a) I'm more than well aware that Jews were not the only people persecuted by the Nazis. But they were the primary focus of Nazi ideology and suffered more than any other group (full disclosure: a great-grandmother was killed by Nazis for being Jewish, though I don't know if it was in a concentration camp, and I'm named after a Holocaust survivor. So I could be more oriented towards their plight. But yeah, I'm very familiar with what they did to homosexuals, gypsies, communists, etc etc etc)
b) I disagree. It is unreasonable to forgive someone who doesn't acknowledge wrong doing. It's nice if you do, but it certainly isn't something which should be expected.
c) you and I are from very individualistic cultures. The idea of collective or shared guilt makes little sense to us. But it is natural in collective cultures. For example, when the Sewol ferry sank in South Korea a couple years ago, the entire nation felt a sense of guilt and shame, and people from all over the country came to the site of the accident to apologize to the families of those lost. And it wasn't out of any sense of duty or obligation. You watch the interviews and you can see true, heartfelt sorrow in those apologizing. So "everyone is already dead" doesn't make a difference to them. And it may even be beside the point when you have living politicians ducking Japan's actions in East Asia (and SE Asia)