I think the key is ATL being an O/D point. KLM and AF from ST along with BA and possibly others from OW fly to IAD despite it being a *A hub. I doubt many people flying to/from there on AF/KL are connecting to domestic DL flights, at least not nearly in the percentages that would at a DL hub. Also note that KL serves IAD with an A330 which is their smallest long haul aircraft (but great for the seats being in 2s on the outside of the aisles).