I think the appeal of the iPhone is that it is marketed like a luxury good rather than a commodity, like the Japanese-made cell phones are. The Apple Store in Tokyo is in the super-ritzy Ginza district, after all. (Although the same is true in the US; the Apple Stores are always in the high-end retail districts, and the iPhone is a luxury where its competitors are faceless commodities that you "pay" ninety nine cents for every two years.)
Another thing I see going for Apple is that, it seems, people in Japan are actually willing to pay for consumer electronics. In the US, we go for whatever's cheapest (go to Best Buy sometime, not a high-end item in sight), but the Japanese seem to be more discerning. At least in my experience.
(I am typing this on a Y30,000 keyboard that was imported from Japan. The most expensive keyboard I can find on Amazon is $100, and only because it has a shit-ton of stupid bells and whistles, like LEDs and a text display. This keyboard is a regular 103-key keyboard without a numberpad. No lights, no display, no wireless. Just a good keyboard. Only in Japan...)