[mkaresh]

The weight difference could be because of how they have to locate the mechanism for a manual window. I've heard that door engineers hate manual windows because they're much harder to package.

And because you probably have to make the parts sturdier to deal with a manual input--much like the driveshaft often has to be thicker on a car with a manual transmission.

Now, some power windows might be manual mechanisms with a motor attached, while others are optimized to be power-operated. The latter are the ones that might be lighter. I have heard that power windows can cost less than manual windows.