Hi @Simon Lloyd
Thanks for the message. I'm familiar with that podcast from Freakonomics, thanks!
While there is some truth to what's being said regarding homes being torn down at what appears to be a rather pre-mature time, especially in comparison to North American homes which may be in use well over 100 years, a lot of the information contained is reflective of theory - derived from a predetermined "depreciation" formula established by the government, in essence, to keep the economy humming.
The basic formula was determined by taking the age of all the homes that had been razed, and averaging out their age. For single family residences it came to 30 years so that's what was used. The life-span for concrete/steel multi-family homes is given at 37 years!
To help set the proper perspective, I'm going to refer you to a couple of very good articles that really explain well exactly what is going on. I could explain here, but it would be sort of lengthy and the articles are pretty succinct.
After you've read them, if you have any questions, please don't hesitate to ask me, either here in the forum or via email or pm.
To be frank, investing in Japan is a pleasure compared to other locales.
http://japanpropertycentral.com/2014/02/understanding-the-lifespan-of-a-japanese-home-or-apartment/
http://www.japantimes.co.jp/community/2014/03/31/how-tos/japans-30-year-building-shelf-life-is-not-quite-true/#
(If the moderators don't allow these links, I'll send them to you directly.)