Maybe because the average height is 5"4 not 6"1 haha ! 120 pounds is optimal for a 5"4 person c:

Hmmm. I wonder if people deliberately underestimate weights? There's really no incentive to be honest. If a friend or acquaintance asks me to guess her weight, and I think it's 250, I would say something lower, because we all know that people feel good to think that they look like they weigh less than they do, esp. if they are worried that they are overweight. Or if a friend tells me her weight, and it's pretty much exactly what I would've guessed, I would act surprised and say that she looks like she weighs less. I would do these things simply because I believe that all my friends look good and I don't want them to be self-conscious about their appearance....