I may sound like a conspiracy theorist but oh well: The cynic in me says such graphs are (figuratively) propaganda by the 1% (of 1% in wealth, not income), in that now we can define what the masses are "ok" with while we, the 1% of the 1%, can accelerate our gains further. Let the rest of them have crumbs and be content.
The cynic in me is actually thinking it's interesting that the Scandanavian countries are left off the charts. They are usually touted as being amongst the happiest countries in the world, despite rather aggressive tax regimes to pay for it. Perhaps there is some cherry picking going on here? Either as propaganda to show that the US is the happiest, or to show that money equals happiness - which might not be true in…
The graph they have included the 25 most populous countries, and is already a mess (lots of overlapping things). The Scandanavian countries didn't even make the cut on that one, the Economist probably took the ones that were the furthest apart. Maybe if all the Scandinavian countries fused together they could have made it?