It is far from sure that the decisions made by human brains rely heavily on quantum effects and that the relevant data can't be obtained by some non-destructive scanning, without Heisenberg-demonic measurements. The Laplace-demon aspects is in fact a matter of precision. If Omega needed to simulate the brain precisely (unfortunately, the formulations of the paradox here on LW and in the subsequent discussions suggest this), then yes, Omega would have to be a demon. But the Newcomb's paradox needn't happen in its idealised version with 100% success of Omega's predictions to be valid and interesting. If Omega is right only 87% of the time, the paradox still holds, and I don't see any compelling reason why this should be impossible without postulating demonic abilities.