Meanwhile, there is a thread on the UA board that DL and UA have just renewed their interline agreement. I suspect UA tosses more passengers Dl's way than AA/US.
While I understand the dispute over rebooking rates, what I don't understand is the failure to allow interline ticketing and bag checking, which is rather unusual, particularly as one can envision a number of scenarios where someone may wind up on an interline itinerary as a result of lower cost or availability.
I don't know or care who's at fault here, but it seems a lose/lose proposition for both AA and DL customers.