Someone in the real world notices fan fiction. Specifically, they measure it using search engine rankings.
Good points, but they make too much of “female substitute for sexuality.” True, I do like that bit about revelation of character, but take slash: a lot of them also show the protagonist (the "heroine," if you will) realizing that they're gay (clichéd nowadays) or discovering why they hated some other character on site: because they loved them and assumed this feeling would never be returned. (Depressingly common IRL.) In other words, it's not all about the hero's character: it's about the heroine, too.
And I mean, come on! Have you read the steamy sex scenes in slash? (And some het?) Substitute for sex??