Attaining a higher cadence in a race gear is achieved by working out with lower gears with less resistance, and turning a higher cadence. Keirin racers warm up before races on rollers, which have virtually no resistance, and can spin the cranks well over 200 rpm. Today I did a workout at the track, and started out with 45 x 16 and then flipped my wheel and completed the workout with a 45 x 14.
As to the importance of upper body strength, think of your body as part of the bicycle. Just as you don't want power loss due to flexing of the bicycle frame, you don't want your upper body to flex because you won't get full transfer of power into the cranks. Also, good sprinters don't rock their bikes a lot, because that also wastes energy. The reason you see some road racers throwing their bikes around during sprints is that they are trying to push outrageous gears, and they are actually going slower than they would if they used a lower gear at a higher cadence.
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