To those of you who "yawn" at the news: he didn't come out for you. No need to read on (or go to the effort of commenting to say that you don't care).
But unfortunately yes: a lot of people do care.
There's the religious fanatics who today are still trying to legislate to deny gay people the rights that they should be allowed to enjoy (heck, look at the number of UK MPs/Lords who tried to block equal marriage last year)
And the visibility does two jobs:
1 - (not so relevant for a CEO in San Francisco) showing the general population that gay people do exist and want to have the dignity that's otherwise denied to them is an important message that helps counteract the sort of legislation I just mentioned.
2 - it shows younger gay people that (a) they're not alone, and (b) they have successful role models in all walks of life.
Did you know that the attempted suicide rate among gay teens is around 20-30%, even in "western" countries? And the % of homeless youths who are gay in the UK and US is somewhere around 30 to 50%.
Surely it can only be a good thing for those young people that they have a hugely successful role model to look up to?