True in principle, but their oil stock would become so valuable that other countries will just decide to grab it, invade Norway, and plunder the whole lot.
The fund does not invest in larger stakes than about 10% per company, I believe, so that would mean pissing off a whole lot of their own citizens too, to obtain amounts adding up to a quite small percentage of their own economy.
There's no reason (once you've decided to nationalize) that you couldn't just nationalize foreign interests (or even interests held by a certain (group of) nations -- such as a nation you're at war with?
