Korean websites have similar aspects. However, Korean websites are slowly changing to be simpler and more visually appealing. Having experienced from Korea, I would extrapolate that Japanese (or Korean) websites are cluttered not because they believe it is better than non-clutter. It's cluttered because most people there don't have expertise in designing a simple and appealing website. In addition, Asian countries tend to be more focused on following the design of their rivals, and since early design is obviously more focused on information than beauty, people follow that. However, if you give a finished product where one is cluttered with information and the other is simple and visually appealing, I highly doubt that people will prefer the clutter.