I was more commenting on the fact that smoking doesn't help.

Generally speaking you don't want people to be hypoxic when they are jumping out of aircraft.

Being hypoxic means your brain doesn't work at the right speed (amoung other things), which can be an issue when your falling to the earth at terminal velocity.

Edit: Clarity

I'm aware.

The elevations I'm talking about are related to people becoming hypoxic when not on supplemental oxygen.

At around ~10-12,000ft the partial pressure of oxygen is low enough that if your not used to it, you can become hypoxic. O2 @ ~20%

If you are on supplimental oxygen (which if you are climbing Everest, you are), in the "death zone" (~26,000ft) even if your are on 100% supplemental oxygen, the partial pressure is low enough that you can become hypoxic. 02 @ 100%

In both cases, if your lungs don't work good (read; if you smoke), you'll become hypoxic at lower levels.