I think people like to buy into the idea of a celeb. Take George Clooney - women loved him in ER and as he was single - well I think many women think 'oooh if I met him' and it helps them to believe in him when he plays the romantic lead.
But if he was openly gay - a lot of people would struggle to see him in the same way playing those types of roles.
They all control their images so carefully now - publicists are very very fierce and apparently the really powerful ones will blacklist journalists if they are deemed to be not nice to any of the 'stars' they have on their books.
Even the straight ones seem to have lots of manufactured relationships.
And without causing too much controversy - I do think that a lot of the US is way more conservative in its views than the UK and thats a big big market