Kate looked very nice naked, but sitting through a three-hour movie just for a glimpse of her breasts didn't seem like a good deal to me, especially since the captures were on the Internet within days. I've never seen Titanic and probably never will.
No, the reason why it made so much money is because it's an epic love story, and girls love an epic love story. Girls would go see it over and over in groups. They'd drag their boyfriends to it, once, but after that it was chick-flick heaven. Leo was at the height of his "he's so cute!" powers, and was box-office gold.