as a high school and college QB, I fell qualified to chime in here..
One of the things about throwing a football well that most people don't know is that your follow-through is different than it is when you throw a baseball...the key is that your hand shouldn't turn over, but your hand should go straight down, almost like a screw-ball follow through with a baseball....the best way to explain it is to hold your arm straight out in front of you with your hand extended out as well...most people tend to have their hand turn clock-wise after or as they are throwing a football, but it should actually turn a bit counter-clockwise...this keeps the spiral "tighter"...the motion isn't as obvious with guys like Gannon whose arm is at all sorts of different angles when he throws, but it is very apparent in over-the-top guys like Favre and Peyton Manning..
Many of you are also correct about a pitcher's power coming from from several different parts while a QB relies more on the arm/wrist/hand, but still uses legs/hips as well, when the protection allows it!