Right, and there are many variants of this scenario that other people can think of. It all stems from the same basic problems above. Punishing cheaters is neces

Right, and there are many variants of this scenario that other people can think of. It all stems from the same basic problems above. Punishing cheaters is necessary, but not necessarily sufficient. The difference from a PoW model is that when mining is essentially free the incentives are different. If it doesn't cost you anything to try it makes game theoretical sense to do it speculatively.