I didn't say I never hit a nail. What I said was I never had a problem. I don't consider your example of hitting an existing drywall nail or screw with a picture hanging nail a problem. Hit it, nail won't go in, move it over 1/2" or so, drive it in, hang picture. You think the typical grandma hanging a pic of the grandkids is going to go searching for drywall nails?
Besides, his stated purpose for searching for the nails is to remove the drywall, a practice I have never seen.