It's probably wiser to let him do it; I don't want to put words in his mouth.
IF I have understood him correctly, he's saying all classes use an interface to use magic. The scroll-writing ability of wizards is a mechanical manifestation of this (in that they can transcribe priest spells into their spellbooks if the spell is also on the ever-growing wizard spell list). For myself, I see the interface in the exact same use of material components for spells, regardless of power source (for lack of a better term); the example I gave earlier is the cleric through faith, the druid through connection to nature, the paladin through devotion, the monk through meditation, the sorcerer through innate power, and the wizard through study...all need the same straight piece of iron to cast hold person. Why should nature demand the use of iron? Your god? How does the iron work with your devotion? Who knows? But it's required.
Now, do most people handwave material components? It seems so. Do most people not bother explaining the interface (though it's right there on page 205 "Instead, they make use of a fabric of magic, a kind of interface between the will of the spellcaster and the raw stuff of magic.")? It seems so as well.
To say it's not in the rules though...no. It is. Even if it's a commonly ignored rule.
I may not be doing his argument justice, however.