The author missed the the main reason why Norwegians are happy, or more accurately, why they have been happy.  The reason is because they are all on the same page.  They have been primarily a homogeneous, non-diverse population that is proud of their common heritage and they share the same goals.  This will change as the population of Norway becomes more diverse.  Then there will be more discontent (like with immigrants that come to Norway for a free ride), crime, cultural clashes and political in-fighting ... and the "happiness factor" will drop precipitously to the level of places like France and the US.