You need an oracle for prediction markets to function. Voting on the truth doesn't work, you will be sybil attacked into oblivion. Is there an oracle present in these contracts? If there is, why wouldn't basic multi-sig work just as well?
Yes, the Oracle problem is the elephant in the room. Augur tries to make it work by creating a new reputation token that accrues to oracles that provide true information (so effectively paying people to be honest), but I'm not sure where development is it - it seems pretty slow.