If you punch someone in the throat it doesn't mean you'll kill them, like nekogami said, to many variables. Now what CAN happen is you punch them in the throat, and what happens to them is their trachea (windpipe) collapses.
In order to heal itself the trachea inflammates (swells) if it swells to much, you basically suffocate. I've seen people get hit in the throat, and luckily they didn't die, but they had just the funnest time trying to breathe, one of them I think actually went to the hospital just to make sure that he was ok.(in the first incident they weren't striking full power, just a freak accident with an elbow strike missing and just landing right in the throat area, again they weren't hitting full force, so this might be a reason why he didn't need medical attention.)
So to play it safe, avoid throat punches.
If it was a matter of life and death for me, I wouldn't hesitate punching or finger jabbing the throat. [IMG]http://www.fightingarts.com/forums/ubb/smile.gif[/IMG]