Saj, I am curious then as to how you feel about the sexist themes in Dracula. Is it more acceptable for teenagers to read that since it has the excuse of being written in a different era with different sensibilities?
Certainly, there are sexist themes in Twilight, but I wonder if there might be more. Having not read the books myself, I can't say how non-fancy-pants people in the text are generally treated (for example, is the damsel in distress ever a mundane male), but it would seem like issues similar to this are present in other, less-distasteful, cultural sources. Consider the superhero world in general: when compared to Superman, the Green Lantern, The Shadow, or Darkwing Duck, the average person in general is relegated to the damsel in distress role. If the only regular person interacting with these superpeople happens to be female, then that would give the appearance of sexism. Thus, is the protagonist of Twilight the damsel in distress because she is a she, or is it because she is mundane?
To offer an illustration of what I am trying to get at, there was an old Darkwing Duck episode called the Planet of the Capes. The premise was that there existed an alien world full of superheroes and that they needed an "ordinary guy" to rescue. In that episode the "ordinary guy" was male, but what if they had been female? It would have given the appearance of a culture entirely focused on the saving of the helpless woman. The reality, however, would have been that the culture was focused on the extraordinary saving the mundane; sex could have been a non-issue.
Might that, then, be the theme of Twilight? The protagonist enters a world of demigods, essentially; being the eternal "damsel in distress" would have been the default of the character even if she was male.
There is something about Twilight that is connecting with a lot more than just teenage girls. To outdo The Dark Knight, I can assure you that a lot more than that single group went to see it. Teenage guys went, middle-age adults of both sexes went, and the elderly as well (I am told that there are "twi-cougars"). Some element in the story, trashy though the trappings of it may be, connects with the reader on a powerful level. I am thus proposing that this element is the desire for the mundane to be connected to the extraordinary.
I propose this because we see it in far more than just Twilight. Part of what made Harry Potter so enchanting was the idea that there was a fantastical world right around the corner that anyone could suddenly bump into. The Matrix also played into this theme, as does Transformers, and even many of Miazaki's films!
There is, however, a difference between how Twilight handles this and how others do. The Wizarding World in Harry Potter doesn't replace the mundane world, it coexists with it. Muggles might only really have the role of the damsel in distress when they make an appearance, but the fantastical doesn’t seek to push it out. In Transformers, the fantastical world fights to protect the mundane world and, on occasion, the mundane can save the fantastical. In the Matrix, the mundane world is at once both a lie and something to aspire to (that is, a world where one isn’t fighting evil robotic overlords). In Miazaki's works often the fantastical serves as a device for discovering the mundane. Twilight, on the other hand, seems to utterly reject the mundane. Once the protagonist is exposed to the fantastical world of sparklies, she is addicted and, like a crack addict, will go back again and again until it consumes her. The mundane has no place in the world of Twilight; it appears to be a story of spiraling addiction.