I'm curious as to why you think dragons kidnap princesses.
A few proposals:
Gold and jewel-loving dragons might just hope to be able to get a few pounds of gold out of a monarch who wants his daughter back.
A dragon kidnaps the princess. A "valiant knight" rides in and "slays" the dragon. A knight might get the princess to fall in love with him, which leads to the knight becoming basically royal himself or at least requiring the monarch to bribe the knight a lot to get him to leave so that the princess can be married to whatever important duke or prince was originally intended for her. Even if the princess doesn't take a fancy to the knight, there'll still probably be some reward. The dragon and the knight split the loot.
Princesses are pretty pets!
Papa dragon's little girl dragon wants a pet. He doesn't think it's a good idea, but when she looks into his eyes, he can't say no. She wants a pet human.
"Alright. You can have a pet human, but you've got to take care of it yourself."
She wants a princess.
"No! Maybe after you've shown you can take care of some peasant girls, you can have a princess."
No one wrote down the peasant girl that got kidnapped to be the little girl dragon's pet, because, hey, who cares? However, she was dutiful in feeding and cleaning and taking care of her, so eventually she got a princess. Awww...
The Princess is slated to be married to the son of the Duchess of Chartreuse. The Margrave of Fuchsia hires the dragon for a hefty sum of gold to make sure that the marriage does not happen, lest the alliance between the king and the House of Chartreuse thwart the Margrave's own plans for the House of Fuchsia to form an alliance with the House of Feldgrau to force a revocation of the Edict of Celadon which would... (conspiracy continues for 75 more pages).
What other ideas have you seen or come up with?
edited 12th Aug '11 2:53:18 AM by Maklodes