Chris.
Doing it mechanically as opposed to electrically, yields different results.
The AFC is entering an altered signal, where as the modded maf is actually allowing more to enter in addition to fooling the ECU. Some how the AFC in line is altering more than just the MAF signal.
I know you understand this from an engineering standpoint, but there are other factors than neither you or I are aware of. The results I've experienced are factual, and it appears the explanation goes beyond the obvious.
In the end, it really doesn't matter why it works, because the end result is that it does.
Perhaps you can figure out *exactly* why it works, but this thread isn't being aided by arguing.