The Harleys I ride have forward controls and shifters that are larger and have somewhat more resistance than the metrics. Thus they affect the amount of surface area affecting the foot. Heavy leather has its own advantages as far as safety goes, but I just find it more comfortable to have some thicker material between my foot and the shifter. Also, at freeway speeds, heavy boots that don't move with lots of wind, also increases the comfort level.
Oh yeah. It looks cool, too.