Disabled people do not have to buy first class tickets. I am disabled, and often am seated in the very back of the airplane. There is a narrow aisle chair (a very skinny wheelchair) to help people get into the plane and through a plane's aisles. Airline agents at the gate often nicely switch my seats closer to the front of the plane, but not to first class. You are claiming some things that absolutely aren't true, here.
I don't think the comment author claimed that disabled people have to travel first class, but that some people with disabilities choose to travel business or first class because travelling in economy is too painful / not practical.
