Maybe it's just that I'm not an adult, but I get the idea that adult readers of romance novels get more of the attitude of "oh, that person likes to read fluffy romance novels". Which is condescending, but not a moral judgment. Whereas teens liking Twilight are given more of "that teen likes fluffy romance books with bad morals". (Though it's probably just a result of which people I hang out with.)

(And then we get into older women who like Twilight, and it all gets very confusing.)