Related to what I said earlier; I'm wondering what hollywood is trying to accomplish with these female tropes/stereotypes, or if they even realize they're doing it.
I think they're appealing to the lowest common denominator among people who like rom-coms. Think about the two main characters of a MPDG film: You have your sad sack of a dude who's basically just an average dude, and the pixie who's quirky and inexplicably single and attracted to the dude.
The guy is actually a pretty shallow character. Sure, he's got trouble, but how does he deal with it? By getting sad and/or running away, and has to be rescued by the girl. As was discussed, the pixie is a shallow character, with no life beyond the movie.
The guys who can identify with the protagonist, I imagine tend to be those who have had bad luck with relationships and/or not had any, who think to themselves, "Hey, that's like me! Wow, if only I could find one of those girls, I know she'd like me and then I'd be happy!" This is obviously a poor attitude to take.
[This part is wild speculation, probably could use a bit more exposition] Then any girls who can identify with the pixie, probably have fairly low self-esteem. They may think that, "The guy in the movie is kind of cute, and ends up being a decent human being! That's my ticket, I just gotta find some sap like that and rescue him, and then I'll be happy!" This also is a wildly poor attitude. [/spec]
EDIT: In summary, the lowest common denominator would be people who have trouble with relationships and/or low self-esteem. There are plenty of
us them.