IMHO it's all nonsense. A vibrating string has a bunch of harmonics, plenty more than the first 10 are still audible. So a conservative example of 10 harmonics all with differant wavelengths, each one has an equal number of nodes to its harmonic number, so the fundamental has no nodes, the 1st harmonic has 1, the 2nd harmonic has 2, ect... By the time you get to the 10th harmonic, there is already a total of 55 nodes on the string, i guess around 35 individual nodes as some will be on the same spots as other nodes. So asuming a roughly even spread thats 1 for every 3/4 inch. Where ever you put the pick up and fret the string there will be a node over the pickup. And thats not even counting the fact that the magnet field of the pickup is probably an inch or two wide. Which anyway will counteract the effect of the nodes.
If you measured the string vibration at the exact point of one of these nodes you would indeed find that the harmonic the node belongs to is absent from the sound. But a pickup is not a single point, it is a wide field, and that node is going to move about depending one where you fret the string.
So there may well be people who swear that they have experienced the effect of these nodes but all I have ever seen is subjective opinion. They may well have experinced some differances from pickup placement, but that could be for a whole bunch of other reasons. The node placment theory doesn't stand up to even basic scrutiny, it has more holes than a Phlagarian Multiwhore from the planet Bonk.
just my 2c
chris