Did you miss the bit of the article where it wsas pointed out that those countries have the highest number of startups in the world?
Not "less on average" but "the most".
Its possible we shouldn't be too quick to infer too much from this article, however. Norway is a major oil producer and if Norway's startup creation rate is very different from Sweden and Denmark's maybe we should be looking at other factors.
Didn't the article mention that Denmark was number 2 in startups after Norway? So not very different at all. And I suspect Finland is quite up there too.
Along with the fact that Norway saves all its oil in a fund for a rainy day, I don't think oil figures that much.