A very, very, VERY tongue-in-cheek and silly observation is how I take that phrase (which I did not create) :
Every man (i.e., especially those I find attractive) I can assume to be gay. If proof exists he is straight, then he's guilty of being the lesser-than form of life for guys and I don't need to know anything more about him. And proof is even questionable as I've had straight-to-the-world guys blatantly come on to me.
If I don't know for sure, there's always hope in believing a guy is gay until he's absolutely proven non-gay guilty. :)
When one is gay himself, it can help to see that others 'out' there are gay, too. Not that they have to be famous like Travolta, but, depending on where an individual may be in life, it may help him or her to know that others are gay, too. As a young gay person (I knew I was gay as soon as the 'feelings' began), it would've helped me to know more other gay people were around.