True LEM you have to consider the use of standard PAX weights through out the globe . And you would have to say that there is alot more overweight departures than realised. Not so critrical with larger types.
But smaller Types like 19 seaters it is and most definitely affects performance. The Beech 1900d accident in Carolina, forced the lifting of standard weights for Adults. Well it isnt a lie that people in the developed world are getting heavier.
Not sure what the actual weight change was but I belive it was 10lbs increase in each category.
Many a time as Captain on Twin Otter I wondered what my actual weight was, even after heavily scrutinizing the load sheet before departure.
I belive I aint alone on that one.