I usually don't enjoy invoking his name, but as you stated, that's his advice and he's absolutely correct. He sees hundreds of thousands if not millions of rounds going downrange each year, so he knows.
Louis Awerbuck also recommends keeping the bolt and carrier wet. In fact, if someone fails to heed this and has trouble, he has been known to make everyone get in line while he goes from student to student squirting lube on their bolt carrier.
I've never cleaned an AR during a class (suprised? ), but I do usually add lube at the end of the day before I pack the rifle into its case. For what it's worth, I use either FP-10 or its successor, WeaponShield on my rifles, but any decent quality CLP or oil will work as long as you keep it wet.
Slight hijack here, but I LOVE WeaponShield on my Bersa. I have tried several different lubes in the last year, and WeaponShield is the first one that I can FEEL a difference with...