Correct, and it ties in with your previous point about the growing purchasing power of the black demographic, which naturally leads to greater attention from advertisers (shocking, I know). And to reiterate my earlier point, the biggest reason for the increase in interracial couples in ads is purely economic. If you are targeting families, and you need to hit all the demographics, it's hell of a lot more efficient to cast one interracial couple than to cast two couples of the same race.
Nothing more, nothing less.