I did a bit of testing with weight when I had a 13.0 second car. When holding everything else as constant as I could and adjusting for atmospheric conditions, it followed 100 lbs = 1 mph pretty well. My 60 ft was always inconsistant so I cannot claim the .1 in et with my data but it did trend in the same direction. I believe if the suspension and driver were better, it would have also showed directly in the et too.

Some people go out at the first hint of daylight and buy all the usual parts to reduce weight when if you just keep a closer eye and mind to things through out the car, you can weight reduce while still keeping it all steel. Makes for more fun in the engineering. Some fenders and or doors might be lighter than you think straight from the factory once you take off all the sound reducer, undercoating, unnecessary brackets, etc. Hoods are a whole different story and yet, you can still keep the steel and gut it just enough to make a good difference.
Also as mentioned, scales can vary, Fuel tank levels, safety equipment, etc form one to another.