They just say that until they realize that when you don't have sex for a week, you want it every day, but after you have sex, the need fades for a while. And of course sex drive decreases with age, from an extremely horny peak around ~20.
I mean, I have sex with my wife on average 3-5 times a week. It's not daily but it comes close. It only changes when she's recovering from giving birth or one of us is sick.