I can see where your coming from David as I too would feel cheated/let down/disappointed if I specifically booked a flight based on the aircraft advertised.
A flight isn't necessarily all about getting from A to B. It forms a large part of your holiday, especially if flying long haul. So, comfort, entertainment, food, service etc are all factors in your choice.
If I booked an advertised Dreamliner flight, I am booking Dreamliner more than 'the flight'. The fact that it was Dreamliner would have swayed my choice of dates, departure point, cost etc because I wanted to experience Dreamliner.
Good luck with your case & please let us know how things are going.
Glynis