Well, it's not outdated to be sure. I'm an Exercise Science major at Ball State U and I hear that you should not sit down immediately after intense exercise. I'm not exactly sure of the mechanism but if I remember right, it is because of the way venous blood returns to the heart. Muscle contraction is a large mover of blood back to the heart by pushing blood past one-way valves located throughout your veins (not arteries). For example, when you finish working out your legs, if you sit down you won't be using your leg muscles so you won't be pumping as much blood from your veins back to the heart. If not enough blood gets back to the heart, voila: your blood pressure drops and you can pass out.
If you ever feel like you are about to pass out from anything, cross your legs and squeeze your thighs and butt muscles. It quickly returns blood to your heart, allowing you to maintain blood pressure to the brain. I promise, it works!