They're 'temporary' because Norwegian employment law allows companies to layoff staff for up to a year to enable companies to cope with unexpected downturns without permanently firing people. A company also avoids having to payout severance packages at a time of financial crisis.
However, if you were cynical & exploitative, I guess it would be possible to hire massively for a project, say a new computer game, and then after release when many of those keen young developers aren't needed any more, exploit this legal loophole and dump your staff with virtually no notice, no severence packages and a promise that 'maybe' you'll get your job back in a year.
Failcom has invoked this law/loophole 3 times after their 3 major MMO releases - Anarchy Online, Conan and now TSW. (I'm not sure but I think they may have done the same thing after the Conan exp).
That's exactly what every company does in the US. It's an absolutely common practice. They hire people for a project and when it's over they lay them off.