Why are the winglets different on A320 and A330/340?
A senior Airbus manager told me during the 1992 ILA in Berlin (where the A340 was making a visit during the initial flight test camapin) that intensive investigations has demonstrated the big A330/340 winglets to be not more efficient than the small A320 ones (taking into account additional weight etc.). However, several operators requested Winglets where they can put their logo on, so the passengers could see it all through the flight. Therefore it was finally decided to install the large ones.