AZSarge,
Actually, it's basic physics (a subject I realize is not everyone's cup of tea). By giving the BB some back spin while it's in forward motion, the speed of the BB combined with the fact that the BB is spinning "forward" on the bottom half would mean that the air being "pushed" forward underneath the BB is fighting the air moving past it due to forward motion. The equates to a percieved slower airflow over the bottom of the BB.
On the other hand, the spin imparted on the BB on the TOP half is being "pushed rearward" (you may have to picture a BB in your mind to get any of this). Thus, when combined with the BB's forward flight, you get a faster moving section of air on top of the BB, creating a low pressure area. And hence, it acts somewhat like an airfoil.
This is similar in concept to a Helicopters blades while in forward flight. Picture looking down at a helicopter from directly over the rotors. Now, make the blades spin counter-clockwise. When the chopper is moving forward, the right side of the rotor would be spinning in the direction of flight. This combined with the forward motion means that the right side blades are spinning faster (in effect) that the left rotors. And the left rotors are traveling slower. This may help you visualize the BB (looking down on the rotors is the same as looking at the BB from the side).
[
] I hope I didn't confuse anyone too badly.