perhaps this is deceptive. i would have to agree with you jill on the blood flow to the hair follicle. in horses, the brushing gets the oil over the hair more, making it look thick, and perhaps not letting the tip dry out.
and just for grins, the spinny comb on a cordless drill works wonders on horses knots and loosens them up. my farrier neighbor is starting to use it for therapy. one interesting thing about the drill is, is that it generates a lot of static and a drill i the electricity came through the handle and startled me. changed drills quick.
The brush not only promotes hair growth but is better at training hair than comb. The comb does not "break" the shaft like a brush does. The brush also will drag the natural oils with it through the rest of the hair.