Dumbledore revealed to be gay

[Dr Mario]

i dont see how defining his sexuality is going to contribute to the harry potter series/w.e. u wanna call it as a whole....

By itself, it would make very little difference (besides adding a slightly different spin on some of the scenes out of Dumbledores past). The real difference is meta-textual and has more to do with social conditions and why she chose to reveal this post-series rather than in the main narrative itself.

There aren't many GLBT characters in mainstream fiction. There's even fewer that are portrayed as anything beyond villains and/or flaming cliches. So when a well-rounded, flawed but ultimately sympathetic GLBT character turns up in a hugely successful book series, it makes waves. It's a role model sort of thing and it's heavily tied to social attitudes towards, and stereotypes of, said groups.

Now, springing this revelation after the series is finished (despite it looking like a long-planned character trait) suggests a lot of things outside the main work. It suggests an author who was afraid to include it for some reason, which in turn suggests things about the society she's operating in.

And that's where all the stupid controversy comes in.

edit: And if anyone thinks that hardline religious folk are the only people who have problems with homosexuals, their opinion is simplified to the point of caricature.