Primary Difference: The punitive nature of the peace at the end of WWII.

Germany lost Silesia, Prussia and Eastern Pomerania, with the population there driven out of their homes, the country was split in two and occupied, thoroughly looted by both sides, and in the West the Coal & Steel Pact brought (West) Germany back into the fold, while giving the other signatories a say in how Germany's resources were disposed of. There was also the creation of NATO and the Warsaw Pact; Lord Ismay, NATO's first Chief of Staff, joked that NATO was there to keep the "Yanks in, the Russians out, and the Germans down."

EDIT: To expand on the answer, the defeat at the end of WWII was considerably more comprehensive. When WWI ended, the blockade was starving Germany out, politically and economically Germany was a mess, the German armies in the West were almost at the point of disintegration, and Germany's allies had begun to abandon it.

In 1945, Germany had been invaded and completely occupied, with many cities heavily damaged by bombing and fighting; the German Armed Forces had completely collapsed, and the subsequent occupation precluded an independent unified Germany being able to revive itself and contest the settlement. the civilian population had also suffered considerably more, relatively, than in WWI, and was well aware of how comprehensive their defeat had been.