I think the arrow drop info on Jackson's is about the mostimpractical info on his site. Worse than impractical, actually, because so many people wind up confusing arrow drop with trajectory.

Arrow drop is not the same as trajectory. Arrow drop is based on launching the arrow dead level with the ground. The arrow is at it's highest point at the bow and begins dropping the instant it clears the rest. If you did shoot the arrow dead level with the ground at 20 yards, it would indeed drop 8" in the time it takes to get there. (Pull of gravity is 35 feet per second, per second)

When you launch the arrow at an upward angleyou've put it on a trajectory.It rises up against the force of gravity, reaches a high point, then gravity starts pulling it backdown.Even shooting at 20 yards, you're launching the arrow on an upward angle. You aim the arrow upward to counteract the effect of gravity, to make the arrow fly upward, arc over, and dropinto the spot.