bob, try this:
put a drinking straw into your both and try to breath through it. now, remove the straw and breath through your open mouth. the larger "intake" of your mouth allows you to ingest more air faster.
IF the MAF was the choke point of the engine, enlarging it would increase VE.
Haha, I don't think it gets much simpler than that. But, if the factory MAF flows enough for the engine, than obviously there will not be an increase in power if you open it up. But, in the event that the MAF is a restriction or "choke" point, then it would only make sense to open it up.