It's not for NA engines man, it's for turbocharged engine. He said trying to keep the intake air colder is the reason for intercoolers in general, not for intercoolers on NA. Which is true.
The air in a turboharged car will be a lot hotter on a turbocharged car (being compressed and having to run through the very hot turbo's intake, so has to be cooled.
Believe it or not, cars will make more power on colder air for the reason he stated: cold air is more dense (has more oxygen in it, therefore more bang - more power).
If you want to see the difference for yourself, just fit a sport air filter next to your exhaust manifold, and see how fast your car will be with that.
CAI will give you a bit more power, if they are properly heat insulated.