Unsure if I'm stating the question correctly, but I know there are warnings against quickly unplugging projectors suddenly because of the damage it can cause to the projector bulb. Is this applicable as well to laptop and desktop power cords assuming that the unplugging is done after powering off the computer?
For any device, it is certainly best to power it down before removing power, as you stated. But once this is done, it really doesn't matter how quickly you remove the plug, only that you pull it straight out to avoid bending the prongs.
When you remove the plug, there is going to be a point where the connection is broken. No matter how slowly you remove the plug, when it hits that point, there is no more power, unless you have a high enough voltage to arc across the air gap.
As for projector bulbs, they might benefit from a gradual reduction in power, but you won't get that from removing the plug slowly; you get that from some special circuitry that can vary the power on power down or power up.