» The Long View on Real Estate - Blog of the Long Now

There is a strong element of hindsight bias in these studies which should be better discounted. The Amsterdam area in question has remained consistently popular over the centuries; the chart would have looked pretty different if it had, say, fallen out of favor after one of the wars it went through. The original author admits as much:

"The thing with Herengracht is that it never fell out of favour during all these years, it was always (and still is) part of Amsterdam’s most attractive real estate."

Choosing several random areas worldwide (including ones which might have been popular at one point but no longer are) and conducting this study over would be a better way to go about it in my opinion.