I understand your point, but I must disagree with you.
If they just levied a tax there would be endless hemming and hawing about how much and it would likely take months. And then the next legislature could rescind it.
This way, they get some recompense immediately for money doled out to Cyprus...AND there's the added benefit that in future people will be much more careful about asking for money. (Also keep in mind that upwards of 50% of the depositors are Russian...the Cypriots seem to have no qualms about the Russians taking over which gives you some idea of the mindset of the people.)