Argentina's justification for nationalizing oil companies

Sometimes one has to wonder if politicians can say certain things with a straight face or if they are that stupid.  Here is Argentina's president justifying nationalizing a Spanish oil company's assets:

Kirchner has argued that the move was justified because Argentina faces sharp rises in its bill for imported oil, and Repsol has failed to make agreed investments needed to expand domestic production. . . . .

If you are a company in a country that is going around nationalizing assets, what does it do to your incentive to make large investments?  Is this really a big mystery?