Originally Posted by
Down Low
BA aren't psychic. There are a many reasons why you might have wanted to book 10E&F. They don't know why you booked a particular seat, for all they know you could have had a friend travelling in 10D that you wanted to sit next to. So when there is an aircraft change you will, generally, still have that seat number assigned (main exception being when the seat you booked doesn't exist on the new aircraft).
Emergency Row was purchased - BA charge extra for this row, customer paid the extra bit, ergo, customer wanted the emergency row. So when they change aircraft, move the person who paid extra for a emergency row to the emergency row of the new aircraft. Not very difficult and no tea leaves need to be read.