Backoffice;
I'm now with you.
In the case of the "Titanic", Cameron & Ballard had a pretty good idea where the ship had sunk, e.g. information provided by surviving deck officers, and positions in which rescue ships located the lifeboats shortly after the event. The "Titanic" being a large ship, had all the utensils, cooking gear, crockery, to hatch covers and boilers, along with anything thing else that wasn't tied down to get distributed on its way to the bottom. Even so, I doubt if the mystery trail which they followed to the hull was very long.
AF447's crash location is much more of a mystery. Potentially the a/c could have gone in any direction for up to 40NM in the time it could have been flying from the Last Known Position. That's over 5,000NM^2, or 17,000km^2 to cover. So to be effective, back-tracking debris (the V/S being the largest and first to be sighted) is the logical way of doing it. Notwithstanding, the current Phase 3 search is programed to investigate between 2,000km^2 and 3,000km^2, but not by a "hit or miss" method, but rather by using a "mowing the lawn" technique looking initially for hull sections, wings and engines. Also remember that anything that has made it to the bottom will have only retained its shape and size if it was solid and non compressible. Seat cushions for instance would be a solid object no larger than a small calculator!
It may well be that they do find something else first, but I doubt it.
The following is a link to a short demonstration video of the Remus AUV in operation mode:-
YouTube - AF 447 search - Seabed Explorer Remus - March 2010
mm43