Thanks for enlightening me. I trust Park on the practical stuff, but their explanation as to *why* it happens strikes me as bunk.
I don't think that this has anything to do with the axle being hollow and thus flexing, but rather to do with a bolt-on axle being under tension (as the bolts are tightened) and the QR axle being under compression (from the QR tightening the dropouts against the locknuts).