First of all, the situation is much more complex than was described. Japan is a highly regulated economy, things that sometimes seem to be obvious to do are often either formally prohibited or more often informally discouraged. I suspect some kind of regulation would be the reason there is no on line Apple store in Japan. I don't think there are any other on-line computer stores in Japan. The most important thing Apple can do in Japan is promote itself and present a product that people want to buy.
Japanese consumers are the most brand concious and best educated in the world.
Advertising and promotion are powerful tools to establish a brand identity. This is especially true with the market consisting of young women. They have a lot of disposable income and could easily afford an iMac. In fact, more than half the iMac customers are women. I've seen trendy magazines with pictures of young women cuddling their iMacs on the magazine covers.