Jim wrote, "As a retired chemist, I appreciate your experiments and respect your results. But as a gardener, I have observed that "acid-loving plants", such as holly, azalea, and blueberry all thrive well when mulched with pine needles..."
Well, I have also noticed that they all thrive under a hardwood mulch as do most other woody perennials. If you're interested in theorizing what it is about pine needles that make them a superior mulch to something else you better try some experiments using both.
Blueberries suffer from drought, holly and azalea suffer from winter dehydration so I would assume most any mulch would be helpful. I would put my money on wood over needles, though, because rottting wood holds much more water than pine needles and also encourages more earthworms.