The difference between post WWII Germany and post-apocalyptic Germany is that there is no America to empty her coffers in order to rebuild Europe this go round. If Germany or any other nation in WWII had to foot the bill of their own rebuilding then they probably wouldn't bounce back so easily. Add in radiation, mutants, and all kinda of other goodies and I think it's pretty plain to see how things get so fucked. Plus I imagine that like most major nations all the important cities likely did get nuked.