NO.

In PWM motor drives, the frequency of oscilallation is usually in the ultrasonic, certainly in the high KHz. If you imagine a high frequency voltage applied to a motor (= inductor) then the current in the inductor starts to rise linearly until the magnetic material becomes saturated. This is a bad thing. So we switch off the current. Now energy has been delivered to the motor, and means are provided to ensure that the current can continue to flow, which it will with a steadily decaying linear ramp. If means are not provided then Watch Out...

So by switching the duty cycle of the input, you can deliver a linearly variable amount of energy to the motor, and you will not see motor speed fluctuations.

Steve