I think Southern Illinois is focused on rural medicine. I heard from people in Chicago that if you're applying from the Greater Chicagoland area, then you have absolutely no chance at that school.
I realize that saying you want to help the underserved is what the ADCOMs want to hear. I saw this in a generic medical school interview video on YouTube where the girl casually said she wanted to help the underserved. If you really have the desire, then you need to walk the walk, not just the talk (or something like that). Don't just say it because you think it will improve your chances. If you say you want to help the underserved and show absolutely no desire based on past experiences, then ADCOMs will see right through you.
Otherwise, yes, many schools do emphasize it more than others.