The grip on the ball has a lot to do with it. The reason that a 4-seam FB doesn't drop in velocity as fast as a 2-seam FB is that that seams trap a boundary layer of air against the ball. That reduces the amount of drag. If an OF instinctively rotates the ball to a 4-seam grip before letting it fly, it will reach it's target quicker and be less likely to tail off line. It's just a good habit to train the guys in at a young age.
Some older guns used to get the pitch speed out of hand while others picked it up after the ball had traveled about 20 feet.
The newer style guns are much more accurate.
obtw: The faster the spin, the less drag you get. So it's a factor of both grip on the ball and how you release it, not just arm speed, but both of those things can be taught to an OF. It's not rocket science...... it relates more to the properties of rotating bodies in a fluid medium. (ok, ok ... maybe it is like rocket science)....