I'm amazed how often I hear the question "What's the business case for Diversity?" (Capitalized because I'm referring to it as a program.) Isn't that like asking, "What's the business case for civility?"
I guess as long as the question's being asked, it's just an indicator of the continued need for the emphasis.
The other thing I've noticed (even in diversity training) is that whenever I've heard people say they think their workplace is "pretty diverse" or doesn't have any diversity problems, they're invariably straight, white folks. I haven't met a single gay person or person of color at any job I've ever had who thought everything was honky dory diversity-wise.