The news/speculation/rumours concerning Job's health unbelievably affects Apple's stock value because he is 'indispensable' for Apple, and deliberately cover up the information regarding his ailment. Things would be different if the corporation can run effectively on its own and independently from any particular peson, and such important information is available on any news channel.

The same logic is also applicable to the situation in Thailand. Any country/corporation that run on one person will face the detrimental fate someday. It's a fact, and everybody knows it, but some try to deny it.