Yes, didn´t mentioned the tons of Exp. you also get. The Wiki says it should be 5000 per hostage.
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It has to be a bug or otherwise wrong implemented thing, because it´s totaly breaks the economy and but not least the "longtime goal" of reaching 20-30 Goldcoins to leave this place.
I mean i play this game for just a week, but i am pretty sure this isn´t intended, compared to how other stuff is rewarded.