I believe you do get a little warning regarding the airport change. Hmm.. just tried to do a search, but can't find any flights that will force an airport change right now..
As I said before, you get a
little warning about the airport changes but it's not very prominent and is easily missed by someone not looking for it. I don't recall the warning specifically telling prospective travelers that they are responsible for transferring the luggage themselves either. Knowing that now, I look for those warnings and book away from those potential fares but it would really be better if that kind of ticketing required a conscious opt-in.