Some people take issue with the word 'pride', because you can't really say 'I'm proud to be straight'. When Tim Cook says, 'I'm proud to be gay' however, what he's really saying is, 'Contrary to what society expects, I am not ashamed of being gay, because there isn't anything shameful about it.'
I completely agree with this interpretation. I'm gay and I don't find it something to be proud of -- same as how I don't find my brown hair or blue eyes things to be particularly 'proud' of. Unfortunately, saying "I'm not ashamed to be gay" may be more accurate but it also feels like I'm agreeing to frame the conversation in terms of whether being gay is something to feel ashamed about. I don't even want that idea tied to it so, in the absence of other options, I'll err on the side of gay pride.
I didn't think it would matter to read this from Tim Cook but it turns out I feel very encouraged by his words. When he says "engineer" among his attributes, well, I'm also an engineer and it gives me a sense of possibility.
Role models are hugely important. I never found Joan Rivers particularly funny, but I noticed on Twitter how her passing truly upset many female comedians. It turns out that funny or not, she was a pioneer as a female comedian and in turn managed to inspire a whole new generation of female comedians who felt, as you aptly put it, a sense of possibility.
That's why if we want to be successful in diversifying the world of programming we need Tim Cook to come out, we need successful women and minorities to be vocal about their passion and work in our field (much more so than the usual narrative of "tech discriminating against X").