Beepster
Okay... look at it this way. Take an unplugged guitar and hit some strings. Doesn't sound like much. Now touch the headstock or any other part of the actual body of the guitar to a wall or desk or whatever. It will amplify it simply through vibration (I used to take my guitar into the crapper as a kid and butt it up against the drywall to practice as I pooped). So we have just confirmed that there are vibrations going through the body of the guitar. Whether those vibrations are going to directly affect the pickups or not would have to be answered by an electrical engineer. HOWEVER what WILL be happening at the very least is those vibrations will physical affect the vibrations of the strings themselves which WILL affect what is being picked up by the pick ups.
Resonance and whatnot.
I Want to Believe!
WARNING! Physics content:
The speed of sound in wood is ~10 greater than air.
Since Hz = cycles/sec and speed is ft/sec, we can get the wavelength of a frequency by dividing speed by Hz to get ft/cycle.
What you will find is that the wavelengths are 10 times longer, and at 2,000 Hz you get a wavelength in wood of ~6.5ft or 2m (and longer at lower frequencies).
So if we are talking about reflections against the edge of the body bouncing back and causing phase reinforcement or cancellation with the strings, how much difference in phase is a body with slightly different dimensions going to make? And keep in mind that the longer the wave travels, its amplitude is going to be reduced, especially at higher frequencies (with shorter wavelengths).
Again, the idea that something might make a difference does not mean that it automatically makes a
meaningful difference