Interesting thought, but the reality of the situation is quite different. If something is in the public domain (i.e. something you can see, hear or smell) what provisions within the realm of the law protect you from using that sensory data? A company's parking lot may have provisions for me not entering it (i.e guard, fence, etc), but if I perch myself on a parking ramp across the street and use a camera with a powerful lens I can still take pictures of cars and people within the lot.

The same is true for radio, and conversely 802.11. If you expose yourself to data leakage via loud APs / incorrect antenna then it should be well understood that that information is being placed in the public domain (i.e. WPA handshake). A would be malicious user is not bound by any of the restrictions mentioned, and so placing them on people that are knowingly auditing is highly counterproductive unless all the client is going for is a warm fuzzy. This particular way of thinking about pen testing and assessments needs to be at the forefront of the testing itself, because if the client is that misinformed/misled they probably need more help than an incorrectly scoped assessment.