Maybe in Reno screws don't rust out but they sure do here in NE.
How long would it take for a drywall screw to rust to the point of breaking in NE.? I can't imagine it would be a concern in my lifetime. I generally use #10 galv. screws but I can't see getting too excited about using drywall screws. My guess is the guy just wan't to find something to whine about.