?!? It sounded like perfectly find advice to me. After all, the specifics of magic in any game are particular to that game and any specific influences it had. If the player likes a particular rationale, that's fine. But it might not fit the game at all.
But as far as finding examples in literature... it's not all that easy to find examples in literature of protagonists who wear armor at all (much less regularly). For most of The Lord of the Rings, the only warrior in armor is Gimli (Frodo avoids most fights even though he is armored). The dwarves only put on armor once Smaug is gone in The Hobbit. Most of the company in The Sword of Shannara, if I recall correctly, are unarmored.
At the rate characters wear (or fair to wear) armor, I wouldn't consider a literary spellcaster out of armor to be particularly definifive.