SofiaAmes, I think you're overinflating those salaries -- and, even if you weren't, saying a circa $50k salary in LA is 'extremely well paid' is ridiculous.
Look: I only responded to your post because you were so rude forthright, and you're talking about two cities I've lived in. Please don't pull that 'you drove through Compton once and got scared by the black people' crap.
I'm not even sure what's enraged you so much: it's not even up for argument that black/white relationships are extremely underrepresented in major studio pictures, and these pictures are a massively visible American export.
A movie like Hitch is a $70 million investment. The American public no longer goes to the movies by rote each weekend; you have to practically drag audiences in. If there's even the slightest chance the central relationship will confuse/appall/anger/alienate the audience, then it's not going to happen.
And that's not the same as saying all Americans are racist -- just, with that much money riding on it, production companies err strongly on the conservative side. And they haven't made the race/casting decision at random: there's obviously a long and horrible history of prejudice against black/white relationships. Again: I'm NOT saying that everyone in the US is against them, but the studios have clearly hedged their bets, and decided that the risk of alienating potential customers overcomes any urge to break the pattern or blaze a trail. (And it's not just about losing the overt bigot vote: it's about all the people who don't consider themselves racist ,but feel inexplicably 'uncomfortable' with a black/white pairing, and then feel sort of angry at any movie which reveals their own inadvertantly racist assumptions.)
(... I keep typing 'black/white' because these unspoken rules of representation don't apply to other interracial relationships.)
It's not even just the USA: these big budget films heavily rely on foreign market sales, too, and so they need to make the movie as 'accessible' as possible on a global scale, ie bland, branded, and with simple laughs and mild violence. Action heros are never gay. Female love interests can be 20 years younger than male protagonists, without comment, but reversing that is unthinkable.
What pisses me off just as much as the wimpy studios, is the way discussion about the race/casting issue gets shot down in America, all the way from 'no, Ross had that African American date on Friends, all the barriers have been broken and now you're just LOOKING for problems' to 'so you're saying that ALL AMERICANS ARE RACIST'. Meanwhile, the same old crap's being churned out by both Hollywood and the ad industry. Did you miss the massive fucking controversy about the Cheerios ad that featured a biracial family? When was that -- 1963? No: 2013. It made the fricking news.