The right wins in Sweden

The alliance between right-wing parties won the elections in Sweden. Göran Persson will leave his post as "statsminister".
The result of the vote is somewhat strange, in the sense that the country does well economically speaking. So why change a winning team?

I wonder if this is the curse of left wing parties: When the economy goes well, the middle class gets better, and sees no need for heavy, costly state wellfare. The middle class is usually the deciding segment of the population. If the left wants to remain in power, it must prevent the economical situation from improving too much, which of course is unacceptable.

I was told the Swedish approach to economy and wellfare was to have high taxes when the economy does well, to have enough funding for difficult times, during which taxes are lowered to favour a rebound of the economy.

Is the new idea short-sightedness, "party when it's time, we'll call in the socialists for help when things get tough"?