Martin already gave a good answer, but here's a few more details with visuals. A QB's throw is like an NBA player's free throw shot. Repetition is key. If your mechanics are sound, you'll have consistent results in your passes. read more
The "throwing motion" greatly effects throwing power and throwing accuracy, as well, of course, delivery time (which in the NFL, a game of milliseconds, is important). Tebow was never very accurate, and had a delivery time almost twice the NFL average. read more
Rodgers is somewhere in between. His throwing motion isn't amazing but the talent and ability is so overwhelming it doesn't matter; he is just a freak. People often confuse throwing mechanics (grip, pronation, elbow and shoulder placement during the throwing motion, wrist snap, foot placement, release speed) with the end result of the pass. read more