I think they are jumping the gun here; this may not be a discrimination issue.
Many people have made these correlations in the past and I don't think the studies go deep enough. It's dead easy to look at a person and say "they are fatter than normal and make less" but so many other things come into the equation.
For example tall people make more but is that discrimination against short people or are taller people more confident and dominating for positions of leadership. Similarly overweight people could be self-conscious with a low self esteem and limit their abilities to manage or lead people. Being overweight could also be an indication of lack of control, poor organization and lack of motivation; all personality related not appearance.
Then there's the chicken and egg argument...what if lower income people eat worse food (ie. more trips to cheap fast food joints); maybe it's the person's income determining their appearance and not their appearance determining their income.
Personally i don't think discrimination is going on here.