IMHO your arguments for a "modern Germany" UA don't quite fit in, since this is a game where Japans UA is about their bushido code... And the list of similar examples continues on and on.
Again, it's about reflecting what is truly a civ's trademark quality. To me, and I'm sure to a lot of others, the first thing that comes to mind when one thinks of Germany is not the ability to recruit barbarians as conscripts.
As Naresh points out, Japan's unique ability is both familiar and a widely recognized stereotype, as well as it fits with Oda Nobunaga, who, if I remember my history, was a central figure in the unification of Japan in the early to mid 16th century. Bismarck holds a similar position in Germany history. He is a typical 'Landesvater', a pivotal historical figure whose leadership laid the foundation for much of what is modern Germany. I believe it would make more sense if Germany's "unique ability" reflected this era in Germany history, rather than some distant past during which there was no such thing as 'a Germany'.
I've vested way too much time in this. Believe me when I say that I don't care that much. I never even play as them