The most enjoyable Japanmanship blog, which chronicles a Western game developer hanging out in Japan, and he's posted about the differences between games in the two regions - as he says: "There is a law that states anyone with a blog... must, pro bono publico, write an editorial" on the matter.

I particularly appreciate this: "Often weird little games like Tokyo Bus Driver or Densha de Go appear in Japan and are looked upon as examples of whacky creativity. They’re not, though; they’re simple wish fulfillment games. Becoming a train driver is still regarded as a dream job by many children (and fathers with unfulfilled dreams)."

The conclusion reached? "I’d say that as a developer you can and should put in certain elements to attract other markets but if you plan to make a fully Japanese game it will be difficult, though not impossible." So, yep, a certain amount of mutual exclusivity here.