I thought the original poster was talking about the fact that the backlight brightness is now settable on the Ipod Video and some others at all (since about two weeks maybe) and not about the settings change which came later - but it's not very clear from reading the post.
The backlight is usually one of the bigger power drainers so I wouldn't be surprised if using a lower brightness would lead to an increased runtime. But as already mentioned, a battery_bench would be most helpful to find out for sure. I'm not aware of someone doing one or rather two to compare before and after.
Edit: After reading again I have to add: yes the estimated runtime doesn't tell and is rather useless, you need proper runtime tests to compare.