Wycombe
The AB 738s are equipped with winglets that according to the blurb in their in-flight mag gives them better take off performance, climb rate, and lower fuel burn. Thats probably the difference.
MO'L probably couldn't bring himself to pay for the extra metal bits at the end of each wing - even though he could have put paid advertising on to them. Perhaps he didn't think of that!
If I'm wrong, please correct me.