Many airlines fly under the United Express name, Skywest, ACA (Atlantic Coast Airlines), Great Lakes, etc..., all operating different aircraft, and probably offering different levels of service. You stated that you flew an ATP and a BAe 146, so I guess you flew United Feeder Service with the ATP and Air Wisconsin with the BAe 146. Since these two airlines are mostly affiliated with UAL, I would assume the service was pretty uniform. Whereas Skywest is partners with Delta Airlines, Mesa is partners with America West and USAirways, etc..., so I would guess they would offer different levels of service.
BTW, I thought that United Feeder Service was going to get rid of their ATP aircraft sometime soon. Does anyone know if they will? Also, does any other airline use the BAe ATP in the United States? I can't think of any other that United Feeder Service.