To book on board with the 10% discount, you must place a deposit on the reservation--10% deposit rather than the usual 20%.
DCL has loads of experience with how to best fill ships including which promotions are likely to fill the ship at the best price in each season or month. THey use this info to determine what group to target with a special...and sometimes they try new specials. They also know how far out these deals need to be presented in order to get the desired response.
There are all kinds of specials open to anyone--IGT/VGT/OGT, kids sail free, etc. Obviously, booking on board is only available to those who are on board. Then there are specials open to only certain groups--Fl resident, CM rates, military rates...sometimes even GA resident and Canadian resident specials are offered.
DCL makes more money on board from first timers and those with relatively fewer cruises than they do from families with high numbers of previous cruises. First timers who can afford it are more likely to buy a shore excursion (they don't know about booking on your own or just doing something like a beach without booking it), a t-shirt (no huge collection yet), photos, spa experiences, etc. People with high numbers of cruises have all the pins and t-shirts they need, know about companies that offer private excursions at lower prices than DCL, take their own photos (or have CM do it), and have had experience with Palo, spa, etc--they will do it based on previous experiences, not feeling like they "must."
So who do they target? All of us! They'll offer whatever specials their computers tell them will result in a full ship at the best price!