I'd also suspect humans on a plane will follow a normal distribution in terms of weight. The aircraft weight/loading is done on an average sized person (which used to be 75kg if I remember correctly). Conversely every motherfucker will load their luggage with as much shit as possible if it's not limited.
No, I demonstrated reading other comments and synthesizing their text into an easier form for those without reading skills. I am not arguing remotely the same point as you are.
The result of your summary was the erroneous conclusion that the extra cost was for more manpower, demonstrating why the airlines are able to get away with making spurious extra costs.
The scanner's part of security, which is potentially shared between multiple airlines with multiple cabin bag weight limits, so it wouldn't make sense as the place to weigh things. It only works if it's done somewhere airline-specific, like check-in or boarding.