[brrt]

Betz's law arises from the fact that you can't very well stop air dead after you've extracted energy from it - it has to keep on moving to make space for new air. (Otherwise pressure would build up indefinitely, a clearly non-physical situation). So it applies to all such devices, rotors or no. (It doesn't apply to fluids because fluids don't compress, but that is a completely different story).

[qyv]

I am no means an expert, but from my understanding you are only partially correct. Betz's law essentially says that because the velocity of the fluid exiting the cross section of the turbine is lower than the velocity or the fluid entering, the exiting fluid must consume more volume, and that their is a calculable limit to that difference. If these devices are in fact using vortices/turbulent airflow to induce resonance then perhaps different rules apply to the amount of energy that can be extracted?