Not true at all. Maybe in yankee land but not in the South. I guess it's more fashionable for you people since there really aren't many blacks in the North so it's considered exotic to you weirdos.
I live in one of the blackest cities in the country, I'm the minority where I'm at yet you never see whites going with blacks. I mean, you might see one couple a year and there's a good chance they are tourists. I would try and look for it when I was younger because I was with a black chick and I would try and see if others were doing the same. The only IR couple I know in person is a white coworker who is in a relationship with a black broad for the past 5 years.
Most people are attracted to their own, that's just how it goes. That's not to say you can't find someone of another race attractive, but that doesn't mean actually wanting to be in a relationship with someone outside your race. The differences in lifestyle and values makes these types of relationships much more complicated than dating within ones race.
Also, the white Male/Asian female pairing that you mentioned was the most common pairing, idk anything about that but I can say that the Asians around me are all Vietnamese and they tend to stick to themselves. Very rare to see of them in a relationship with a non Vietnamese.