Tim Cook didn't have to speak up. There's been speculation about his sexual orientation all over the media for a long time, and it's not as if something was suddenly leaked. By all accounts, Cook is an incredibly private guy who would, all else being equal, rather not talk about his personal life at all--ever. He writes a little about this:
I don't consider myself an activist, but I realize how much I've benefited from the sacrifice of others. So if hearing that the CEO of Apple is gay can help someone struggling to come to terms with who he or she is, or bring comfort to anyone who feels alone, or inspire people to insist on their equality, then it's worth the trade-off with my own privacy.
Yes, hearing that the CEO of Apple is gay does matter. But even more importantly, it matters that he's not apologetic or conciliatory. Instead, he writes that that being gay is "among the greatest gifts God has ever given him." This is precisely the kind of affirmation that queer youth--heck, queers in general--need the most.
Thanks, Tim Cook.