As far as my outsider's knowledge goes, many Americans choose to build 'cheap and lightly' with resulting lifetimes of less than 20 years.
Your "outsider's knowledge" is wrong, unsurprisingly.
See the-age-of-the-housing-stock-by-state to get some real information. And, if you read the article, you'll see that the states with lower median housing age are those with higher growth (i.e. building a lot of new homes because the population is growing in those areas - not because they're replacing existing homes).
The only places I've seen homes/apartments actually being ripped down and replaced is where the location is more valuable then the existing building and the replacement is larger - this is mainly done in wealthy suburbs where smaller houses are being replaced with much larger ones (and then the small homes were usually built in the 1950's or 60's).