The maf is a MEASUREMENT OF ACTUAL AIRFLOW coming in.
Think of it this way...
Guy at gate of stadium = MAF sensor
Guy seating people = Motor
There is a guy at the front of a stadium with a watch and counts how many people are walking in the door.. If the rate of people coming in the door changes the guy counting and watching his watch will still report back how many people are coming in, regardless of why. These people can be getting pushed in, or the people could be less restricted to their seats after they get in the door, but the guy at the gate is JUST counting air coming in.
The guy seating people is your motor.... The cam makes your engine seat people faster, but there are still just as many people to seat. The cam makes for less congestion after people get in the door so more people can get in, and the guy at the gate will count more people going in.