NVIDIA drivers on Windows have an option to scale on the GPU instead of on the monitor, though I'm not certain whether they ever default that on. Presumably it's there as a workaround for people with bad/broken monitors. It'd be interesting to try and measure whether that option raises power draw...
I've never had an NVIDIA driver with it on by default. I've run two different computers with NVIDIA GPU's through a TV and had to manually scale the picture on both of them when I couldn't get the TV's auto scaling to work properly.
