If I understand what you wrote, the double negative means that you think the "extra penetration effect" is in people's heads. Assuming that I understood you correctly...
Maybe. While few things beat a properly done, double blind, controlled clinical study, there is a lot of anecdotal evidence to support at least a difference between high and low frequency zappers (in terms of their effectiveness in certain areas). Is the difference significant? Is it being correctly attributed? Don't know. The pool of reporting persons certainly is biased toward positive results (someone else already addressed that), but I'll accept that *something* is different.
Why is another question. I don't think it has anything to do with skin effect, for two easy reasons and one more difficult. First, the difference in skin depth is very small, way less than an inch, and would not explain the magnitude of performance difference being reported. Second, the body is not a single conductor. The vascular and lymph systems resemble an interwoven mesh of lossy conductors, not a single strand of copper wire. In fact, skin effect is *reduced* in this kind of situation. This is why high frequency power transformers are almost always wound with stranded wire. The individual strands, even when touching, present a lower impedance to high frequency current (compared to a single strand of equivalent cross-sectional area).
But my main problem with the skin effect argument is that it is contradicted by experience. As anyone who has owned a cordless home phone over the years knows, higher frequency means *more* penetration, not less. Over the last 20 years, the transmitting frequency has gone steadily up, over 20000-to-1, from 47MHz to 5.6GHz. With each generation, the transmitter power goes down and the range goes up. Same for police/fire/commercial walkie-talkies. And let's not forget the microwave oven. Yes, the transmitter power is hundreds of watts, but the penetration through a frozen turkey is actually pretty even, nowhere near the unevenness predicted by the inverse-square law.
Skin depth relates to electron flow, not photon flow. IF (a really big if, with zero hard data after over 10 years) the zapper's effectiveness comes from the electromagnetic field (ala microwave oven), and not from electron flow (ala light bulb), then many conventional analyses fall apart.
But I digress. My opinion is that the performance difference is more attributable to the difference in frequency spectra between the two types of units. The low freq units have many more harmonics, including a large number which the original zapper can not produce. On the other hand, the low freq units have significantly less energy at the higher harmonic frequencies. There are several people on these forums who have frequency generators capable of helping to figure this out. I wonder if they have done any testing of their own?
There also is a vocal "frequency doesn't matter" contingent. Something about frequency must matter, because nowhere in Clark's books does she recommend pure DC. It always is pulsed in some manner, creating a fundamental frequency component and harmonics. Back to those folks with real frequency generators, I wonder if any have tried zapping with a single freq sine wave? Unlike the Clark zapper, it could be offset so there is no "negative" output. Now *that* would advance our understanding of zappers.