I'm curious to hear the other side of the story. As with most ZOMG THE HUMANITY!!!! stories like this, each side embellishes and the truth is somewhere in the middle. I do find it curious why a seat exchange was not "allowed", but again I'd like to hear both sides before I start throwing stones.
Pax who needed an aisle chair for boarding were boarded first at AMR, and they were not necessarily seated in any one location or another in the plane. Non-ambulatory pax are boarded via an aisle chair, a narrow gray wheelchair that is hard to maneuver, difficult to use, and not at all comfortable for anyone involved. However, until someone comes up with a better way to board non-ambulatory pax, it's the best we've got. The aisle chairs are VERY narrow (they have to be, to fit down the aisle) and it's damn near impossible to wheel one of those down the a/c aisle without bumping the seats, at least a little, at some point.