When I was in Tibet last July I talked with the inn owner where I was staying, and she told me that most Tibetans who have lived on the plateau their entire lives will get sick if they go down to sea level, and have a hard time adjusting.
One thing the article stated incorrectly is that there is 40% less oxygen at high altitude. This is untrue and most people make this mistake. The amount of oxygen is the same at all altitudes where humans reside, but the difference is the pressure and therefore the concentration. When pressure decreases, for some reason your body becomes much less efficient at extracting O2 from the air, so it needs time to create more red blood cells to increase cellular perfusion.