Power & torque are directly related through time & RPM. It's like speed vs. acceleration, there's an extra integration step with respect to time. When it comes down to it, at any given speed, 30, 60, 80kph, there's a certain amount of power required. In order to generate that power, you can use high-torque/low-RPM or low-torque/high-RPM.

Problem is you max out how much torque a human can generate since the leg muscles can only exert so much force on the crank. Then in order to get more power and more speed at 100% leg-exertion, the only thing you can do is increase RPMs once you're pushing as hard as you can. So as john bono said, the pros aren't that much stronger, but they're more coordinated and smoother so they can exert higher average torque through a wider percentage of the 360-degree pedal-stroke than us mere mortals....and do it at higher RPMs... resulting in more power & speed.