I agree, I don't think it's necessarily because of racism coming from the produces, casting directors, writers, but just plain fear it won't be successful, and let's face it, everyone in Hollywood wants success.
Even Shonda Rimes knows it, Grey's Anatomy has to have as its leading lady and man caucasian actors, and the majority of her supporting cast is a minority. One asian, three black, one latina. I'm just glad ABC is taking the chance cause Shonda's next show has been picked up for mid-replacement and the leading actress is black.