Well, I think weight is part of it, yes, but I also think that just generally looks are considered. I think it's just that people consider fat "ugly." I notice that a lot more people are nice and friendly to me when I've got my hair done, I've got my makeup done and I'm dressed nicely. I have noticed before that salespeople are rude to me though. It drives me nuts and I just want to say something to them like "Is there a reason you're looking at me like that?"
On the flip side, as I work in a clothing store, I can say that I am truly nice to every customer not based on looks. That has less to with the fact that I am fat and more to do with the fact that I'm a human being and realize that every other person who comes into the store is a human being.
*whew*