I am not one to say that trims/haircuts/dusting makes hair grow or increases growth rate. But I do believe that immediately afterwards, the workings underneath the scalp that are responsible for hair pushing through the epidermis is stimulated for a brief period, especially when the various phases of growth are factored in.
If any of you ladies are familiar with gardening, you know that pruning (cutting) forces new buds to emerge elsewhere along a stem. Pruning is used to shape a shrub and the new growth causes the shrub to fill in instead of just growing straight out. Within days after pruning, there is new growth, whereas the plant's growth was virtually imperceptible before pruning, but we know it had to be growing, right?
I believe that it is somewhat similar with hair. Even though the hair itself is purportedly dead, there are muscles, blood vessels, glands, etc that are all a part of the hair shaft underneath the scalp, where growth actually takes place. Remember, new hair begins before we can ever see it. How does the new hair know? The hair only stops growing when there is damage to the scalp and/or any of the parts within or beneath it. Just because a hair does not contain nerve endings or other vitals does not mean that a cut hair will not respond. A damaged, broken hair would not respond the same way BECAUSE of the damage. The human body is a miracle in every way, shape and form, so there may be more to this theory than we would like to think.