Quoted from Zitt:
Okay boys... don't make me separate you two.
Vireland is more right here... He has valid point about soft woods and real wood screw pitches.
hocuslocus is also right; in that Stern uses the same sheet metal screws throughout the game... that in of itself doesn't make it good practice... this about bom management and higher volumes to get better pricing for said screws... not about what is the right thing to do.
Like you say Stern may use these sheet metal screws on underside of playfield to hold a light socket that isn't moving. But not on cabinet