To one up you - i find it bizare that you think that's the bizare part.
The entire point of a corporation, as a governance structure, in general is to limit liability for its shareholders. That's true for all corporations not just facebook. Its the reason people establish corporations instead of running businesseses informally as an individual.
The only surprising thing is the cost benefit trade-off here seems a bit much. Its not surprising that the facebook corporation tried to do its entire reason for existing.