Electric engine power over RPM
There's a good solid guide to motor power curves here: http://lancet.mit.edu/motors/motors3.html

Basically there are two ends of a quadratic curve at which power is zero. At zero RPM, the motor is stalled and exerts maximum torque force (and will draw a large current, the "stall current" listed in the datasheet). It doesn't actually deliver any power to the load because it's not moving, therefore no work is done.

At the other end, there is no load on the motor and it spins freely at its maximum RPM. It doesn't deliver any power either, as there is no load.

There is a maximum power delivered at half of the no load speed, in the middle of the torque curve.

As you say, the ability to deliver high torque at zero and near-zero speed is extremely useful, and is why motors have been used for power conversion in diesel-electric trains for 50 years.