Its not just people who don't look "sick", airlines also won't help out people who "look" like they need help. Just my experience:
Many years ago, my grandparents came to visit us. They flew from Central Wisconsin to Alabama. My Grandmother was in a wheelchair from a stroke, while my granddad used a walker.
They flew Northwest and arrived in Minneapolis to change planes. When he booked the tickets, my Grandfather had specifically told them of the need for help for him and my Grandmother, explaining their medical conditions. The Northwest rep assured him that someone would be waiting for them at the gate at every step to help them out.
They get to the gate at Minneapolis, deplane, and no one is there to help them. They wait, thinking that someone may have been running late. No one shows up. My Grandfather asks the gate agent for help, and the agent say that he can't help them and that he should have asked for help in advance! So my Grandfather pushes my Grandmother's wheel chair one handed through the airport, towing his walker with the other hand, and both of them dealing with their carry on bags.
When they arrive at our airport, everyone has left the airplane, but no grandparents. No one is there to help them. Since this was pre 9/11, I ask the gate agent if she would like for me to help out my Grandparents, and the gate agent (obviously stressed over this) agrees. So my Dad and I go out on the ramp, get on the airplane and help my grandparents off.
When my mom found out about no one from Northwest helping them after they requested help, she called Northwest and tore them a new one. Needless to say, on the way back home, there were multiple people at every step of their flight willing to help them out.