First off, good question.
I honestly think that between the Axis powers, Germany gets 80% of the attention. I've heard various academic theories, like that Italy didn't and couldn't do much and that Japan and Germany didn't really care too much for each other and that they were a means to an end; I've even heard one of my professors suggest that there was/is a racial issue Americans (Caucasians) and Japanese (Asians) and that Americans didn't really hate their fellow Caucasian Germans. It can't say that I agree or disagree with it though, but right or wrong she (my professor) had a good case.
Anyway, I think that many people focus on Germany for a few reasons:
1: They were incredibly powerful. While I generally don't like to further what-ifs, if Germany hadn't made certain decisions, who knows where we'd be today. She had a powerful air force, navy, and highly profecient ground units. Defeating Germany was not considered impossible by the Allies, but rather a task that everyone knew would take a lot of lives and a long time to accomplish. Same goes to Japan. They were a tenacious enemy that didn't give up easily and lived in a society that practically worshiped the warrior spirit. And to those that study war, that is a characteristic that people look at almost in the hopes to replicate because a strong warrior spirit breeds good warriors.
2: I don't know how much this has been accepted internationally, but here in the US, our forces from that war have been called the Greatest Generation and are studied intensely. I think that within that research, like you said, "know your enemy" kind of plays on here and serves to give a larger picture to what the Allies countered.
3: Finally, and this is completely in an academic sense, I think that writing about Germany is simply easy. One of my professors, when discussing a topic for a Soviet military history paper asked me why I didn't want to write it on WWII. I replied that World War II has been written to death. Like Shakespeare, It is a challenge to find some thing new to write. Most academic writing is is simply one academic agreeing or disagreeing with another academic and listing the reasons why. Academic professors are "encouraged" to write (read: semi-unofficial job requirement). So they look at what they can write about and since most good historians attempt to look at the roots of the problem, essentially Germany in the case of WWII, then it is kind of easy to see where the writing comes from. As for interest, I am not so sure that - academically - it could be read as interest so much as that there really isn't all too much else available.
EDIT: I don't entirely believe that view that nobody wins in war. While no one may win, usually one side comes out for the better (don't confuse that with winning) WWII is a perfect example of this, given the boom of the '50s

Jeff