In the U.S. they've done studies on this sort of thing with children. Female children will identify with both male and female characters and enjoy reading books with either as the protagonist. Male children will only identify with male characters and will only read books with male protagonists.

(Statistically speaking, of course; individuals vary.)

It's one of those things that's very interesting but makes me want to beat my head against a wall; it's now socially acceptable for women to want to be men, but still not okay for men to want to be women.