[Alchisiel]

I have found something Thengal that may help you understand why Legolas was a good shot. It's a paragraph from The Hobbit. I believe that Legolas was from Mirkwood is that right? If so this paragraph would explain things then:
Chapter 9-Barrels Out of Bond-
"There was no thought of a fight. Even if the dwarves had not been in such a state that they were actually glad to be captured, their small knives, the only weapons they had, would have been of no use against the arrows of the elves that could hit a bird's eye in the dark...."
The elves mentioned here are the Wood-Elves from Mirkwood. So it is possible that's why he could off all the fantastic throat shots.