Dynaryder appears to be comparing the weight of a 5 speed hub with the difference in weight between a single speed and 6 speed, and there's no logic to that at all.

Incidently, my Brompton continues to feel far smoother since switching to a 14t sprocket. If anyone is finding the drivetrain a bit rough on a 3 speed and are using the lowered gearing then switching to 14t / 48 or 47t might improve things.