Believe me, I had a hard time with this also. My own argument is what convinced me. Look at the picture of the distributor. The rotor and reluctor are locked together. This by itself means that the trigger and rotor will always be "in sync" with each other.(as long as there are no external retards)
Since they are mechanically locked together, and the pickup coil and distributor housing are basically fixed in place.(assuming no vacuum advance moving the plate) Then the only thing that can happen is they will all stay in sync with each other.
Now what does happen, is everything below the plate moves to a retarded position. (When viewed from the ignition pickup's point of reference)
What is important is the point of reference.