As long as there are not traction issues, this statement is false. Think about it, the DA drops, the air gets cooler, and your car picks up a little power due to it....for a 14.0 car, that might make you pick up a tenth or more, for a 9 second car, that same "better air" might pick you up a few hundredths. In other words, the faster car will be more consistent.
Case and point, one of my fellow racers (Camaro) runs between 6.12-6.08 (1/8 mile) from the heat of summer to the cool fall air....my other buddy (Challenger) runs runs anywhere between 8.9 and 8.5 on the same race days. For those that don't do 1/8 mile racing, in a 1/4 mile that is a 9.5 car vs a mid 13 second car.