A good article from the Japan Times on Why good Wi-Fi is so hard to find in Japan.
In Japan, most demand for email and Web access outside the home has long been satisfied by mobile phone features such as NTT Docomo’s i-mode service, which began in 1999. Years before the age of the smartphone, on i-mode and its competitors, over 70 million users — the same amount as PC Web users —were enjoying Internet access through their phones (there were some limitations, but it was still the Internet). Flat-rate data plans (which only became common in the United States with the introduction of the iPhone in 2007), became available in Japan around 2004, and people began to do everything Net-related from their cellphones. For these users, there was no need for a network of free Wi-Fi at shops and cafes.
Instead, what people in urban areas of Japan wanted was to access the Web while they were on the train to work. People who spend 3 to 4 hours on their weekday commute boosted the cellphone-Web infrastructure. Making a simple Wi-Fi network within a cafe or store may be an easy task, but offering Wi-Fi to hundreds of thousands people on trains is not realistic. Cellphone access might not be as fast as Wi-Fi, but cellphones are capable of being connected on high-speed trains.
But what about tech-savvy Japanese who want to use their laptops everywhere? For them, third-generation (3G) cellphone network data services are available fairly cheaply.