I live in the UK. When my house was built there where only 31 states in the USA. I wouldn't consider this unusual for my neighborhood. During my visit to the states, Massachusetts, buildings that where considered "really old" over here would be considered "well I suppose its old really if you think about it, but not in comparison to the local pub". You get the jist.
Where my Grandparents live; houses that have been up for 30-50 years are being torn down and rebuilt. As such they live in a street where most houses have been built in the last 15 years.
The difference between my area and my grandparents area is they had the shit blown out of it during WWII and my area didn't. As a consequence the area in which they live was rebuilt rather hastily in the 50s and 60s. Poor planning, building techniques, materials and added social change has meant that these areas where awful to live in. As such these areas are being regenerated.
I have no idea what things are like in Japan, but I would imagine this could be a possible explanation for "houses being built to last 30 years at most". Maybe they where built to last, but it's time to change and move on.