So you're saying:
In the admittedly casual observations you've made, you notice far more white women with black men, as opposed to couples composed of white men with black women. Further, you wonder what if it's even a true observation, and if so, what forces come together to make that happen?
Here is a link to a 16 page study on "Marital quality of African American and white partners in interracial couples." I just finished reading it. One thing I took away from it is that interacial marriage is different for those in them, than couples from the same racial background.
If it means anything, the sample in the study were: "52 African American male/White female and 24 African American female/White male"
As to whom you find attractive, that's your personal preferance. Nothing more or less.