Just seen this thread and it covers three very important issues for me.
1) Airlines view mileage redemption as at their discretion. If they accept a redemption booking they will move you onto alternate services if they cancel your flight. This is what they did to the OP. Moving to a red eye via RDU is a poor choice, so I would have asked for a routing from LGA via ORD as they still fly a daytime ORD-LHR though it is a two class 763. They are under no obligation to incur expense but to offer you a reasonable alternative.
2) BA have charged for free award tickets for years. After many years of complaining, I believe that some European flights are now without surcharge but they treat their frequent flyers as revenue opportunities rather than loyal customers. BA will give you nothing for free and even charge their frequent flyers surcharge when they fly on AA metal. BA FF's seem to accept this and the elites are satisfied with perks like lounge access at all times which is only available to elites of AA on international travel.
3) IATA sanctioned that airline surcharges could be hidden under taxes and charges under member pressure to get these charges through with minimum opposition. All airlines charge them for revenue fares but only a few like BA (and some US carriers) charge them on Award Free Tickets. It could be seen as dishonest to call them taxes as they do not go to government or revenue authorities but the coffers of an airline but as I said IATA has mandated this is how they are shown on fare breakdowns and tickets. If you ask for a breakdown of taxes and fees you can clearly see the airline portion and these fees and taxes on some coach fares are substantially more than the "fare".
Do not blame AA for the business practices of British Airways or the requirements of IATA. That does not mean you cannot blame AA for stuff that is down to them like canceling 142. I for one avoid BA long haul and now fly via ORD (giving me an opportunity to see friends in Chicago. The in Airport hotel at ORD is very convenient for early morning departures.
Other AA flight attempts to push me to BA such as the alterations to the LHR-LAX route and missing the same day Hawaii connections mean I either change 3 times via ORD and LAX or I fly UA.
To a prior poster, swapping metal is not reasonable to me, I will swap carriers and alliances before swapping to BA longhaul. The BA hard product is inferior to AA 77W's in Business and First, the service and food on AA have improved dramatically whilst BA's (particularly on flights not from LHR) are now really bad.
I think AA see pushing people onto BA as a win win so they can free up 772's to have the first class cabin removed and the new Business and MCE (and presumably 10 across Coach seating) installed. I suspect the numbers will show something else.