> Who wants to have a mortgage on a house that is going down in value every year?

I do. That's how housing works in Japan - you buy a house to live in, not to save money or invest. Older houses have lost their value (largely due to perceptions of danger in old housing stock - until the last decade or so, increasing understanding of earthquake/tsunami safety meant that houses wouldn't meet current building codes)

That (combined with adequate housing stock, less zoning restrictions, and negative population growth) means that even in the biggest cities, housing is fairly affordable. You buy a house because you want the control and the permanence that comes from owning a house.