Exactly, specialization... America is far, far better than Japan at producing TV shows (think Japs could ever produce something like the Sopranos or Rome?), and it irritates them that gaijin think all their culture is is anime, manga and video games.
Which is understandable, but to be honest - Aren't most countries known by their pop culture image? America and McDonalds for example - I mean, I didn't know America had things like a real cuisine until recently.
You cant blame people for not knowing every facet of every country's culture.