Leezyjet, I was half kidding. I know passengers are not individually weighted and as long as the averages are well chosen and no serious "anomalies" turn up, this works out well. (Although I did hear about a study done in the US that suggests that the averages that are used there are way too low...) (And this woman was hoisted up to the aircraft using a hydraulic lift. Perhaps she would have been weighted, as she would be counted as freight instead of passenger? - Don't these hydraulic lifts have scales built-in?)
But the problem is when you get a very heavy person on board, put it completely up front and still, for load calculations, assume that she is only 70 kgs, you might just be surprised when predicted performance (in this case nosegear compression, probably) don't come true.
As I said, I was only half kidding. In an airliner one fat person alone would most likely not be heavy enough to cause problems with the nose gear. Particularly since it took 20 people from the front seats walking all the way to the back to solve the problem. But it does remain a funny coincidence. But if this were to happen in a GA aircraft or bizjet, one heavy person can (and does) make a difference.