From the information blurb on the page:

    "The highest median income in absolute terms is earned by software engineers 
    in Switzerland (ratio 1.21) followed by Norway (81,400 USD) and the 
    United States ($76,000 USD). Norway has the highest GDP per capita (99,574 USD) 
    in this list with software engineers median income at about 82% of it."

Due to oil incomes and other stuff, Norway tends to be a serious outlier in many cases when it comes to economic metrics.

Although Norway does have high GDP per capita, http://www.bloomberg.com/visual-data/best-and-worst/highest-... said 99,574 USD is Average annual income. That's unfortunately not true according to http://ssb.no/en/arbeid-og-lonn/statistikker/lonnansatt/aar/..., where average annual earnings last year for all sectors is 489200 NOK, i.e. 77824 USD. (Meanwhile, the earnings of programmers, according to http://ssb.no/en/arbeid-og-lonn/statistikker/lonnikt/aar/201..., is 52900 * 12 NOK = 101021 USD.)

It's kind of unfair to compare annual earnings of programmers directly to GDP per capita. If you actually compare it with the annual earnings of all sectors, the ratio for Norway is close to 1.3.

Norway has very high GDP/Cap , the fourth highest in the world. A Norwegian company could probably outsource software development to the USA as a cost saving exercise. My guess is that most Norwegian software developers (that make good money) are employed in the oil industry.

It's actually not as high when you look at it at PPP. It's actually lower than USA at PPP. But that's irrelevant to this question.