No argument there Bazza, I'm not suggesting otherwise however, lifting a weight for just one rep is a demonstration of strength not muscular size.
Lift heavy for reps if you want big muscles.
I totally agree, reps/volume builds muscle but a 1rm and say a 10rm have a pretty strong correlation. It's just easy to ask 1rm to get a gauge of were they are at. If they have a squat 1rm of 50kg safe bet they are not repping much either. Time to just get strong.